Very hurt, need advice.

I am currently taking care of my mother in law, I am a Nursing Assistant and have been for 3 years (also going to full time college for nursing). My mother in law has ALS and I’m just hurt because she treats me only like her caregiver and not her daughter in law. She expects me to do all these outrageous things for her, and is very demanding about it. If she doesn’t get her way she gets really pissed and guilt trips people. She doesn’t care if I am sick or if I am busy. She has aids that come in everyday to help her and I told her that I won’t get as much time as she would like me to be there for her because of school, (I have to drive an hour 4 days out of the week), homework LOTS of it, working, and plus being pregnant. I’m just really upset that she really only treats me like her caregiver. It just really bothers me and it’s the hardest thing ever. I don’t know what to do or how to bring it up to her. I’m not really happy atm and just have a lot of stuff going on in my life. I’m stressed out and just depressed as hell and its just making it a little worse.