I had a few female friends who went on BC for various reasons when we were teens. Nobody thought for a second that they were loose girls; they had valid medical reasons for being on birth control. I went on birth control when I was 17 because 1) I wanted to be used to it before I headed off to college and 2) I had heard it was helpful for women with painful menstrual cramps. It definitely is, and I have stayed on it since regardless of being sexually active or not.
My mom and I had to deal with a lot of similar sorts of stuff when I was a teen due to my incredibly painful periods; I think the key for getting through for the both of us was a lot of open and supportive communication. I still remember going in for my first exam and having the doctor ask my mom to leave the room so we could talk in private; I was completely befuddled as to why the doctor might want to do that. She asked me if there was anything I wanted to tell her now that my mother was gone, and I said no. She seemed puzzled by that, and I explained that there was really nothing I couldn't or wouldn't say in front of my mother. My mother knows nearly everything about me, and always has.
Shani, I think Amanda is so lucky to have a mom like you. I know what a rock and a lifesaver my own mother was, and I am glad that she has you to be that for her. I wish you both the best in getting through this. These problems are by no means easy to deal with, but somehow we get through them.
