Sorry to hear about your mom.
I guess that being that your Mom is fairly stable right now may be the reason the doctor is holding off with treatment. I would say the most important thing is to have a good neuro, really good. One who is well versed in Myasthenia. There are some good links above to start reading. With M.G. everyone is different.
I would ask the doc what he intends to do, what further testing has your Mom had, or going to have. Be familiar with the list of drugs to avoid, there are many. Heat can make you worse, you cannot overdue.
A good neuromuscular doc can help sort out what is M.G etc. Did she have a chest Cat scan. Usually contast is contraindicated.
As with M.G. the biggies to look out for are any breathing and swallowing problems. I hope your Mom's case stays mild and limited. M.G. is tricky though and just keep you eye out for other issues.
I have had years of no meds{not diagnosed} and then went through other treatments, some aggressive. Right now I take high doses of Mestinon, trouble with other treatments and am pretty limited. Everyone is different. This is just a start for you. I am sure others will offer help, the board is a bit slow. I hope this helps and your Mom.
I would say though at some point, treatment is started. Sometimes one also weighs the risk of the treatment also. ps try to avoid crowds, sick, colds coughs etc. M.G. is made worse by many things. I hope this helps, if you would like more info, links, we can help out too. Best to your Mom and family.