Abby, I hope your Aunt will be okay!
There are CMS's that show up later in life. And since MG is autoimmune, it can show up anytime it wants to.
Does your Aunt stay hydrated enough? A lot of older people do not. If they have a pre-existing circulatory issue, being dehydrated will just make that worse.
Of course, there are other things that can cause balance problems like vitamin deficiencies, tumors, inner ear problems and loads of other things.
I hope they'll figure out what's going on.
Annie