Here is what I know about motorized wheel chairs:
The tires are VERY VERY EXPENSIVE and wear out quickly. One thing that we did was to put to a thick layer of electrical tape in two strips on each tire, so the tape would wear rather than the tires. Medicaid only pays for one set of tires each year, so my BIL figured out those tape strips help make the tires last longer.
You probably will want to work with her primary care provider and her physical therapist to help get insurance to pay for it. If its required medically, they will refer you to a reputable provider.
My experience with wheel chairs is from when I lived in WI, for my nephew (who has since passed away); so I don't have a local recommendation for you, sorry.