Well, that's a tough one.... yes, the choice should be given to the girl for sure to have an abortion or not, however, the problem here is our society, where they love to label stuff as halal/haram or in this particular case legitimate or illegitimate, and the ensuing stigma(s) that never leave a person (mother/father).....
In my personal view, fix the god damn society or immigrate to a more tolerable one, instead of killing an innocent soul...........
Here I quote the Holy Quran: (Al Maidah - 5:32)
"Because of that, We decreed upon the Children of Israel that whoever kills a soul unless for a soul or for corruption [done] in the land - it is as if he had slain mankind entirely. And whoever saves one - it is as if he had saved mankind entirely. And our messengers had certainly come to them with clear proofs. Then indeed many of them, [even] after that, throughout the land, were transgressors."
Does the scripture (don't quote me Hadees, I don't have faith in any ONE of them), discriminate between a grown man, a child or a unborn infant? No, it doesn't. So why do we? Answer is simple, we are enslaved by society, not by Islam's teachings.....