I have a question about about abortion?

Im not sure how we got started talking about this me and my friend was having a disagreement about it. I know its a hard one question. In some cases a women has to like rape. Lets say a sixteen year old girl is on birth control and has sex and gets pregnant. is it wrong if she has a abortion? when i was 16 i didn't know that u can get pregnant on birth control. some kids don't understand. Just like u cant drink till your 21there's a reason. what do you guys think?