U don't need top earn the respect of someone like that. Children are a blessing from Allah, regardless of their sex, so just concentrate on ur daughters. MIL's like urs really iritate me, and they are so pathetic....do they not know that the world would stop if everyone was of the same mindset as them and only wanted boys.
And if you really want to give her answer when she blames you for having daughters instead of a son, tell her that the sex of a child is determined by the father, not the mother, so she should talk to her son. (Sorry, if ur husband is a nice person, but he should be standing up and fighting ur side, rather than let his mother treat u like this!)
Epilepsy should not affect ur daughter communication, so I would suggest you join her up in a playgroup which would allow her to interact with children of her own age. If she's still not better, then talk to her consultant perhaps dose of her medication might need to be altered. Also, if you have enrgy-saving light bulbs in the house, you should remove them as they can trigger fits.
Excellent Mashwara.