Hey man, I hope you're alright. Try to calm yourself first, not being able to transition is really rough and I feel you on that. But you know what you are and who you are inside, it's not some wacky devil messing around in there. Hell, I've been told by my mom that I must be possessed or something. Moms can be hard to handle like that. But things will be okay.
If she comes into her room, let her talk and listen if you want to attempt to address what she's saying, but it really doesn't sound like you are going to be able to get through to her with reasoning. So it might be best to just smile and nod, and if you have long hair, that could be useful for disguising a pair of earbuds hooked up to a music-playing device. Just sayin'

Trust me, listening to some good tunes is much better for de-stressing yourself in an already stressful situation than taking in all this negativity.
Do you see a therapist? If not you might want to, they're awesome at listening if you need someone to vent to in person, and might have even better advice to offer. Though if you ask your mother about this, be careful- don't let her talk you into seeing someone who can "fix" you.
Try to squirrel away whatever money you can into a bank account, small things add up. Hopefully that college education will help with job searching, and when you land a job you can rent a place, maybe even save up by sharing a place with a roommate or two. Once you get your own place, there is nothing that she can hold over your head to keep you from transitioning. I can only hope that when you're on your own and she has to decide between acceptance and her own beliefs, that she chooses in favor of her son. If not, she's really missing out.
Just keep your eyes on the path in front of you, and try not to let her get you down. It sucks that parents reject and hurt their own children over faith, but unfortunately there are people like that out there. Hopefully one day that will all change. Good luck, man.