Sorry that this happened to you. Alfredo Sauce makes me violently ill too. Is your mil that uncaring in everything else she does? Or is she just a bad cook ?
I have had a doctor tell me to "wear a depend and get on with my life". People who aren't affected by this condition just don't understand. No matter how much you try to inform them. I hope things improve for you, until then, meet them at a restaurant where you know you can eat.