Hi thank you for your question. Please remember to RATE my answer OK SERVICE, GOOD SERVICE OR EXCELLENT SERVICE so I can get credited for my time.

I am sorry to hear about your situation. Best scenario would be for you to adopt her as your child provided she is under the age of 18 and you would not need to meet the current financial threshold of 18,600 gross earning per year. You would however need to provide adoption papers as well as meet the maintenance and accommodation requirements.

Your adopted child must show that they:

are not leading an independent life;
are not married or in a civil partnership;
have not formed an independent family unit; and
are aged under 18

Please see the following link on how to legally adopt a child who is outside of the UK:

http://www.ukba.homeoffice.gov.uk/sitecontent/documents/residency/intercountryadoption.pdf

Once you have adopted the child the form you will need to complete wold be form VAF4A. The form and the guidance can be found at the following link:

http://www.ukba.homeoffice.gov.uk/visas-immigration/partners-families/citizens-settled/children/applying-visa/

If she is over the age of 18 then the following would apply:

The requirements to be met by a person seeking indefinite leave to enter or remain in the United Kingdom as the parent, grandparent or other dependent relative of a person present and settled in the United Kingdom are that the person:

(i) is related to a person present and settled in the United Kingdom in one of the following ways:

(a) parent or grandparent who is divorced, widowed, single or separated aged 65 years or over; or

(b) parents or grandparents travelling together of whom at least one is aged 65 or over; or

(c) a parent or grandparent aged 65 or over who has entered into a second relationship of marriage or civil partnership but cannot look to the spouse, civil partner or children of that second relationship for financial support; and where the person settled in the United Kingdom is able and willing to maintain the parent or grandparent and any spouse or civil partner or child of the second relationship who would be admissible as a dependant; or

(d) parent or grandparent under the age of 65 if living alone outside the United Kingdom in the most exceptional compassionate circumstances; or

(e) parents or grandparents travelling together who are both under the age of 65 if living in the most exceptional compassionate circumstances; or

(f) the son, daughter, sister, brother, uncle or aunt over the age of 18 if living alone outside the United Kingdom in the most exceptional compassionate circumstances; and

(ii) is joining or accompanying a person who is present and settled in the United Kingdom or who is on the same occasion being admitted for settlement; and

(iii) is financially wholly or mainly dependent on the relative present and settled in the United Kingdom; and

(iv) can, and will, be accommodated adequately, together with any dependants, without recourse to public funds, in accommodation which the sponsor owns or occupies exclusively; and

(iva) can, and will, be maintained adequately, together with any dependants, without recourse to public funds; and

(v) has no other close relatives in his own country to whom he could turn for financial support; and

(vi) if seeking leave to enter, holds a valid United Kingdom entry clearance for entry in this capacity; and

(vii) does not have one or more unspent convictions within the meaning of the Rehabilitation of Offenders Act 1974

Please note the term "most exceptional compassionate circumstances" the threshold for this is extremely high and the applicant would need to have sever medical condition or in a position where they would need urgent mental/physical attention to enable her to meet the threshold.

The applicant must, as a result of age, illness or disability, require long-term personal
care: that is help performing everyday tasks, e.g. washing, dressing and cooking;
• The applicant must be unable, even with the practical and financial help of the
sponsor, to obtain the required level of care in the country where they are living
because it is not available and there is no person in that country who can reasonably
provide it, or because it is not affordable there.
• The entry clearance officer must be satisfied that the applicant will be adequately
maintained, accommodated and cared for in the UK by the sponsor without recourse
to public funds.
This reflects the intended thrust of the current rules applying to parents and
grandparents aged under 65 and to all other adult dependent relatives using the route,
including those aged 65 or over.
The UK sponsor will not be required to meet the new financial requirement of a gross
annual income of £18,600 to sponsor an adult dependent relative, who will continue to
qualify for immediate settlement in the UK. If the applicant’s sponsor is a British citizen or
settled in the UK, the applicant must provide an undertaking signed by the sponsor
confirming that the applicant will have no recourse to public funds, and that the sponsor
will be responsible for their maintenance, accommodation and care without such
recourse, for a period of five years from the date the applicant enters the UK.

The following evidence will need to be provided in support of an application for leave
to enter as an adult dependent relative:
• Evidence of the family relationship: Evidence of the relationship between the
applicant and the sponsor will need to be provided, e.g. birth or adoption certificates.
The entry clearance officer will need to assess whether other evidence is needed.
• Evidence that, as a result of age, illness or disability, the applicant requires
long-term personal care, that is help performing everyday tasks, e.g. washing,
dressing and cooking: Medical evidence that the applicant’s physical or mental
condition means that they cannot perform everyday tasks. This must be from a
doctor or health professional. Under paragraphs 36-39 of the Immigration Rules,
entry clearance officers have the power to refer an applicant for medical examination
and to require that this be undertaken by a doctor or other health professional on a
list approved by the British Embassy or High Commission.
• Evidence that the applicant, even with the practical and financial help of the
sponsor in the UK, is unable to make arrangements for the required level of
care to be provided to the applicant in the country where they are living:
(a) evidence that the required level of care is not, or is no longer, available in the
country where the applicant lives. This could be from a central or local health
authority, a local authority, or a doctor or other health professional. If the required
care has been provided through a private arrangement, the applicant must
provide details of that arrangement and why it is no longer available.
(b) evidence that the required level of care is not, or is no longer, affordable in the country where the applicant lives. If payment was made for arranging this care, the entry clearance officer will ask to see records and an explanation of why this payment cannot continue. If financial support has been provided by the sponsor or other close family in the UK, the entry clearance officer will ask for an explanation of why this cannot continue or is no longer sufficient to enable the required level of care to be provided.
• Evidence of adequate maintenance, accommodation and care in the UK: The
applicant must provide a signed undertaking from the sponsor that the sponsor will
maintain, accommodate and care for the applicant adequately for five years without
recourse to public funds. In addition, the applicant must provide evidence from the
sponsor that the sponsor can provide the maintenance, accommodation and care
required, in the form of any or all of the following:
(a) Original bank statements covering the last six months;
(b) Other evidence of income – such as pay slips, income from savings, shares,
bonds – covering the last six months;
(c) Relevant information on outgoings, e.g. Council Tax, utilities, etc, and on support
for anyone else who is dependent on the sponsor;
(d) A copy of a mortgage or tenancy agreement showing ownership or occupancy of
a property; and
(e) Planned care arrangements for the applicant in the UK (which can involve other
family members in the UK) and the cost of these (which must be met by the
sponsor, without undertakings of third party support).
• No unspent convictions: The applicant must not have any unspent convictions in
the UK or overseas.

As you will note the requirements to be satisfied in relation to some one older than 18 are much harder than someone younger.

I hope this clarifies your concerns. If so kindly rate my answer positively so I can get credited for my time.

Kind regards