Has she actually been referred to an otolaryngologist?
They will prescribe therapeutic head movements for her to deal with and minimize symptoms from what you described as crystals in the inner ear. Otherwise there are other causes of dizziness
She needs to have an ekg to see if she has an arrhythmia. Atrial fibrillation can come and go and when present results in decreased efficiency of the heart in pumping blood. This decreased efficiency and decreased blood to the brain can cause dizziness and lightheadedness
She also may need to have a tilt-table test to see if she has orthostatic hypotension - which is a disorder where people aren't able to compensate with increased heart rate quickly enough when the stand or sit up and therefore the amount of blood reaching the brain decreases for a short period of time causing dizziness which will resolve.
If she has had CT and MRI examinations of the brain then they likely ruled out any localized sinus or ear infection that could cause her symptoms.
Also, if she is on any medication for high blood pressure the most commonly found and likely reason for her dizziness is that she is being overmedicated. As people age their doses need to be addressed. It is not uncommon for people to need lowering doses of antihypertensive medication as they age. This actually is what happened with my grandfather. After lowering his dose of a medication his dizziness and "odd feelings" and tiredness improved completely
Any time you decrease blood flow to the brain you can worsen any balance issues or dizziness.
So she needs an EKG, to have her orthostatic blood pressure taken in the office, if needed after that a tilt-table test can be ordered, and also if on antihypertensive medication she needs to have her doses reassessed by her physician if there is any way to decrease them with short-term followup to make sure her blood pressure remains managed despite a decrease in medication.
That is the best place to start from.
Does that sound like something you can do? Does that answer your question/did I provide good service?