What do you think would happen if you just looked at her in the eye and said:
"Look Mom, I've been taking care of a very sick child, and I'm legitimately exhausted. Why are you pretending to be sick yourself just to gain my attention? You've been doing this for years. I recall perfectly well that for major events in my life, you were always supposedly sick. Do you realize you need treatment for this pathology?"
OK, I realize you might not come out with that
I've said something similar to my mother, who is crazy, although the issue is slightly different. It was in a moment of desperation when her behavior was relentless and truly impacted our lives, in a very negative way. She denied all of it and had a fit, but she toned it down somewhat afterward... because she knew I was on to her.
I'm sure these people realize at some level what they're doing, but obviously can't control it well, and do their best to deny it, even to themselves.