I am in the position where I kind of feel uncomfortable telling her to leave me alone outright since its technically her house.
(Incoming velvet hammer warning)
Sure, it's her house. Where is it written that she is your Empress or Queen and that you must swear fealty to her like a medieval serf? Where is it written that she is allowed to denegrate you and castigate you and generally treat you boorishly and she gets a free pass on having to remain decent to you because of some Saint who lived hundreds of years ago?
I have a very very religious (as in born-again, over the top, extremist) coworker. She also has coping issues and turned to religion. Many times when she gets all snarled up and in a state of hissy-fit, I will remark "I'm sure that's exactly how Jesus would have handled that situation." (in a neutral tone). That's me.
For you, how you choose to handle the situation is obviously your choice. It is her house, she is an adult, you do not have to take this just because it is her house. You are HELPING HER, were she more sane, she would be grateful for the help, not dismissive.
And even if it is "in her house", that does not give her the right to be dismissive or obnoxious to you. What it *does* do though, is gives you the ability to say "sorry mom, I have to go now, this is not at all pleasant and I don't appreciate it. I'll be at home if you want to call me" (and if you have caller ID, only answer the phone if you feel emotionally ready to hang up when she starts with either the guilt trips or the religious conversion stuff or whatever)
The key to making this work is that you must clearly define your boundaries. "I would appreciate it if you might recognize the work I'm doing to help you." "I would rather you didn't try to convert me anymore, I'm an adult, if I'm not Catholic yet, I probably won't ever be. Please stop."
Then always have an escape plan. If it's on the phone, tell her that you don't like being treated this way and she can call you back when she doesn't feel the need to do so. If you're in her house, tell her you're leaving until she can respect your boundaries. Then leave.
You do not have to play a part in this. She is not your responsibility, especially if she seems to show no desire to take any responsibility for herself.
For the record, my 1st ex-brother-in-law was an alcoholic and drug addict. He gave up the substances and replaced them with God. I liked him better on drugs, he was easier to deal with. He eventually gave up God and went back to drugs. *shrug* As long as I don't have to deal with him, he can destroy his life however he'd like.