Thanks for your question.
The key here is being able to prove that the transfer of money to her was by way of loan and not a mere gift. If you are confident that the text messages, or other evidence you can produce (your witness statement and those of any others who have knowledge), can prove that it was intended as a loan then you can have a reasonable expectation to get your money back.
In the first instance you should write a formal letter to her outlining the facts as you understand then and requesting that the money be paid to you (or a repayment plan suggested) within 7 days of the date of the letter failing which you will issue a claim in the small claims court to recover the monies.
If no response is received you can issue through www.moneyclaim.gov.uk, it's pretty cheap (somewhere between £50-100.00 for this, which you can claim back) and very easy to use.
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