She has come to the right place. As a true friend consider finding out as much as possible about the man she is mad in love (not infatuation). From a neutral standpoint, you could be the best judge as it will be difficult for both the parties involved to be without prejudice. For girls this age, physical attraction out shadows everything worth considering in the institution of marriage. Take a decision and if need be send her back to her parents place.
It may sound primitive however in cultures it is still observed have the highest success rate of marriages.