What kind of idiot would hire a health care worker that's so fat she needs a scooter to get around? Aren't there minimum fitness standards where you work?
Of course, it may be that she's one of those professional "victims" who use the Americans with Disabilities Act and other laws to shake down companies for bogus lawsuits....in that case, your boss may be too afraid to stand up for you.
I work for a company that has allowed severely obese people to use 'handicapped' parking spots, simply because they are obese. When I was 385 pounds, I never used the handicapped spots. I had pride, which explains why I am now 140 some pounds less. Some folks don't have pride, which explains why they got to use the handicapped spots.