I am so sorry for your loss and extend my deepest condolences. The sensation of perceiving motion when there is none is a specific type of dizziness called "vertigo" and it is one I am very familiar with, unfortunately. I know how distressing and disabling vertigo can be; I empathize with you and with your daughter.
A bit of background: The body regulates balance three ways: the inner ear, the eyes (what we see) and the central brain which puts it all together you could say. If one of those systems are "off" and the other two cant compensate, vertigo will result.
The problem is, people have many ideas and theories, but no one knows for sure why people get vertigo, and online no one can determine your exact cause. Here are some possible causes.
Possible reasons why people get vertigo include migraines, but usually the vertigo is followed by a headache, though there can be migraine vertigo without headache. Often in migraine vertigo there is extreme visual sensitivity; flashing lights, patterns, and high contrast can make the person feel miserable.
There is also cervical vertigo, which is not well understood at all, thought to arise from injuries or trauma to the cervical vertebrae. I am wondering if the illness that she had involving her neck and base of the skull may have triggered this.
Head trauma can cause vertigo as well. This does not seem to describe your daughter, and it is why I asked.
A condition called Meniere's disease can also cause vertigo, though that is usually accompanied by ringing in the ears and temporary hearing loss.
Tumors of the inner ear called acoustic neuromas can cause vertigo, but they to are often accompanied by ringing and at times hearing loss.
The most common form of vertigo is benign paroxysmal positional...meaning that on sudden movements of the head, spinning sensations develop. That can be a result of little sediments that deposit in the inner ear canal. That your daughter feels worse when she moves may make this a possibility, but the sensation is more described as spinning.
Vertigo also can be a sign of multiple sclerosis.Onset here is typically sudden, and the person with MS will find themselves unable to move their eyes towards their nose, ie look inwards. This does not seem to describe you.
A rare brain defect called a chiari malformation can result in vertigo.
Vitamin B12 deficiency can result in vertigo.
Bacteria and viral infections as well can cause vertigo. That was the case in my situation, and why I asked if she had any sickness; the strange illness she had that involved pain in her neck may qualify; it may have disturbed the nerve that regulates balance.
Last on my list is anxiety; anxiety can cause a whole host of symptoms in people because of its affect on the body. Anxiety should be the last thing that is considered as the cause of your daughters vertigo; physical causes should first be ruled out and I think your daughter needs a very thorough medical investigation.
Treatment depends on the cause, and the cause is determined by knowing the history and the results of a physical exam. In Menieres disease, often a diuretic is given, as well as a low salt diet as salt is thought to be one of the culprits. In BPPV, exercises can be prescribed to settle the sediments in the inner ear. In vertigo caused by bacteria and viral infections, steroids and valium (when the vertigo was truly bad) can be used, in addition to Meclazine (sold OTC as Bonine).
The length of time it lasts is very dependent on the cause. Some vertigos are remarkably easy to treat while others can be more difficult. Vertigo caused by a cold normally lasts a few weeks to a few months (or longer) for the truly unfortunate.
The specialist you should see is an ENT (ears, nose, and throat) physician. Neurologists can help as well as vertigo can be centrally caused; which may well be the case here. Even though glioblastoma is not thought to be hereditary there still may be a propensity for a central cause to her vertigo.
There ARE tests that can be done to pinpoint where the vertigo is coming from (central vs. inner ear) . They include things like ENG's and Rotator Chair and Caloric Testing. Those all look for specific abnormal eye movements called nystagmus; the pattern helps determine where the vertigo originates. MRIs can be done as well, those look for structural defects (like a chiari malformation, or, may it not be so, a tumor). If you have not seen an ENT I recommend you visit one in addition to a neurologist as this has been going on a long time and you do have a family history of glioblastoma.
Treatments can include the above medications, and there are also special vestibular rehabilitation specialists who give exercises to help retrain the brain and help it rewire and correct whatever damage the vertigo did, if there is a vertigo present. There are also visual therapists as well should there be a optical cause or exacerbating factor to the vertigo; as is in my case.
What I would suggest is that make an appointment with your doctor and discuss all this, (as it may not even be vertigo...it could be something entirely different; if she feels better after eating she may have low blood sugar issues, for example) and a referral to an ENT or neurologist as needed; when there you can discuss vestibular therapy and see if they think its appropriate for you.
And absolutely vertigo can cause nausea and vomiting; the sensation of disequilibrium is that disorienting. Its possible her dark urine is due to a little dehydration as vertigo makes it very hard to eat or drink. I am happy blood tests have been normal as dark urine (very dark) can be a sign of kidney damage.
Here is a useful website regarding all things vertigo: http://www.dizziness-and-balance.com/disorders/index.html
I really and truly hope I was able to help, and that your daughter feels better soon