As someone that also went thru this; there is nothing you can say or do to help someone feel better. You can only be there for her.
It took me a few years to get over the loss... And that is even after I did have my son I did conceive two months later; so this helped me. I made sure to cleanse my body as I was toxic due to medications from a cold at the time and drinking from a Halloween Party when I had found out. So I gave everything up and dealt with my friends chiding me for it. (so much for their support!)
What did help me (not to sound corny or anything) was after I started my massage classes... There were two instructors that talked often of Angels. I read one of the books that one spoke of often. I found a passage that really put that part of my heartache to "rest".
*"Very often, I talk with the spirits of children wh stay with their mother following a miscarriage or abortion. The children are happy and well-adjusted and simply want to be with their mother to help and guide her. Or, if their mother gets pregnant again, they may have 'first dibs' on inhabiting the new body and be born as a healthy baby. Those who don't have the opportunity to be reborn grow up on the other side, at about the same rate they would have if they had come to full-term births. Aborted children hold no grudges, by the way. Their souls are as intact as ever." * (I am positive this applies to any child loss, not just miscarriage and abortion)*
This is the ONLY THING that helped me and as soon as I finished reading it; my son came in my room and said "I love you Mommy!" and ran of to play...
I understand this sounds insane to many, but I have become a believe since those days - especially with my work. But you could share the above with your friend as I think that would have helped me more than the rest that you always hear. (or just be there... Your choice!)
Good Luck and many prayers!