Okay this stuff makes me real mad: You have 2 daughters mashAllah. Their sex and/or health is out of your hands, your husband’s hands and your MIL’s hands. And it’s out of every single person’s hand.
But your MIL is upset you have daughters and one of them has epilepsy. It’s YOUR daughter, YOUR daughter’s epilepsy - who the hell is she to get upset and how dare she blame you!?
It’s really, really, really nice of you to want her to like you and accept you but seriously woman, you need to focus your attention on bigger and better things. 
Nothing you can do about your daughters or their health. Nothing she can do, either. Unfortunately. So please do not feel like she has some sort of an authoritative position to accept or reject your doings or that her satisfaction is necessary.