First off, I'm sorry to hear that you've lost your father, that's difficult and really complicates the process of waking up from this cult. If you do (and it's your decision, and one I would encourage you to consider thoroughly) tell your mother what you've decided, it might be beneficial to state explicitly that you're not abandoning her personally. This might be difficult to hear because the cult has been designed such that she will take it personally, but it will probably help to be said outright.
I too would encourage you to seek higher education once you graduate highschool. It's tremendously valuable in exposing you to different ways of thinking, along with different cultures and philosophies. It'll also give you a good chance to start making new friends and building a support network, which you're likely to need in the coming years (assuming that most of your existing friends/family are in the cult as is often the case).
You know your mother better than we do, so only you can tell when the right time is (if ever) to tell her that you want out. I suppose it also depends on how much of the cult you can put up with in your life. If you expect that she'll withdraw any financial support for your education or housing, then it might be wise to wait a little while if you can.
If you were baptized as a minor and never pioneered or had any special privileges after you turn 18 (sounds like you're not going to be doing any of that anytime soon haha) then it might be worth looking into trying to get your baptism annulled. There's some information around here on some that have done this and it might be worth looking into (I haven't looked into it much since I was baptized at 19).
Lastly, I think it's important for someone just learning TTATT and summoning the strength to do something about it to remember that you can trust yourself. So much of the cult is designed to instill self-doubt, and it's tremendously damaging. I wish you the best of luck with this ridiculously difficult situation.
