you clearly have an agenda. i don't know what happened, but being pregnant at 15 is scary, and if you let your feelings about the abortion show to her in the way you are showing them on here, tbh it's no wonder she feels venemous towards you. At 15 she probably needed support, but also to make her own decisions about the termination. In my opinion, her decsion on whether or not to become a mum should take higher preceedence over you wanting a grandchild or not.
she may have broken his heart before, but i assure you, relationships break down for all sorts of reasons, not usually limited to 1 person. Maybe it wasn;t rigjt then but it is right now?
also, there is nothing saying you will "have to go through" another abortion. perhaps again the timing might be right for them to start a family. if that is the case, it might be better for you to be the bigger person and make it up with her because if they do stay together and start a family it will be nice for you to be involved, rather than ostracized