Autoimmune issues are very frustrating. My sister exhibits multiple types. Some have no outward symptoms but others do. It can be difficult to have empathy with someone who looks healthy and complains all the time.
My sister had flares for two decades before her condition became chronic. She would be healthy and active most of the time and then she would suddenly come down with a strange illness that would persist for several months. She would then bounce back and resume a normal life. This was especially devastating for her as a single mom because she often lost her job after repeated flares. Each episode was treated as an isolated event for years. Things spiraled down pretty far for her.
It all came together about 10 years ago when she had a flare that attacked her nervous system. We had to move her in with us for three years. She could barely walk, had difficulty with her bodily functions, severe dizziness and had terrible tremors and tics. She will never fully recover from this flare.
Her most pressing current problem is a heart arrhythmia issue and fluid retention.
The list would get real long if I described every flare in detail.
Very few of her conditions are noticeable but she is not the robust person that she used to be. I have watched her quickly lose muscle tone and mass with each major flare.
Another frustrating thing is that she can be perky and healthy one day and then won't be able to get out of bed for a week. Then she will get up one day like nothing was ever wrong with her. You cannot use the good days to discount the bad ones.

Step back from today and consider your mom's condition through the years. You may see signs. She may have seemed like a real pain because she was in real pain but thought it as just a normal life condition.
Yes, I do believe that many people take advantage of an autoimmune diagnosis. Sometimes, I am sure that my sister is overreacting to certain normal aging conditions. (She is 51) But the point is, I know that she does have this condition even if I cannot always see it.

On the bright side, my sister is now married to a wonderful nurturing guy. The problem is...they moved to Texas! She is in Atlanta to visit her 2 month old granddaughter this week so I will get to see her this weekend!

My prayers are with you and you mother.