What do I say?

My husband and I are blessed with an awesome amazing eight year old son, we have been ttc for over 2 years. My little sister (25 years old, still little to me) has a two year old beautiful little girl and just found out she was pregnant last month with her new boyfriend. This is shocking because three months ago she had what she refers to as a "pregnancy scare" with some other guy. She was so excited and so was I, a little jealous, but she said how this time is different, they are moving in together and going to get married. Last week she moved her and her daughter out of his house because they were arguing about how late he stays up at night. Tonight she called me and told me she made an appointment to get an abortion next week, she doesn't want to be with him and she doesn't want to "share" another kid with someone else. I tried to talk to her about waiting, just a couple weeks ago she was going to marry him. But she said she doesn't want to talk about it she already made her decision. She knows how bad I want another baby, what do I say to her so that I am still being a supportive sister, I know she has to be going through so much pain right now, I've had her back through everything, what can I do for her? And how can I be strong enough?