Welcome to the boards, dark_sunshine.
As a longtime (decades and decades now!) abortion activist and sometimes-worker, I've often wondered and worried about how situations like this go for the children of pro-life/antichoice activists. I can only imagine the level of conflict you must be feeling.
It's interesting you mention that if you had an unwanted pregnancy, you think your mother would want you to choose to terminate your pregnancy: that's actually pretty common, that people who rally against abortion would or do make very different choices in their own lives. Just about anyone who has worked at an abortion clinic will tell you that it's not uncommon to see someone outside protecting the clinic wind up inside of it seeking an abortion at another time, and then going right back to protest it (and likely without telling anyone they themselves were provided abortion care at the same clinic) weeks later.
By all means, as an organization and as a community, we're very strongly pro-choice around here, which for us means that we think everyone should be fully able and supported to make the whole range of choices one can make with a pregnancy: abortion, adoption, staying pregnant, delivering and then parenting, and the diversity in all of those three options.
I can't tell you why your Mom feels the way she feels: that's only something she can tell you. I wonder if your first step with all of this might be to see if you can start that conversation? In other words, maybe before you tell her you don't want to go anymore, that you don't like going, or that you're sexually active, you ask her this question, why she feels the way she does? Is that something you feel able to start with?
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. - Margaret Mead