I've definitely been there! This is a great opportunity to cement your friendship even deeper. If the two of you can get through this, there will be a loyalty there that will be hard to break. It's easier said than done, though, and it takes both you and her.
For me, the most important thing has been to be able to be really honest with my friend about how I'm feeling. Making a habit of covering up honest emotions to avoid hurting feelings is a mistake, IMO. But, this has to be coupled with a sense of balance. When my closest friend was pg the first time and I'd been through 6 years of inf and had been waiting to adopt for a year, I was really into emotional honesty, and I think I made the mistake of pouring out my soul just a little bit too much. She was kind enough to stick with me through all that, but it must have been very overwhelming to her to be constantly hearing about my pain and knowing that she was contributing to it. So, I would say, keep a journal in which you can pour out your thoughts and write your most difficult feelings. But still be honest with her about how you're doing. Don't pretend that it doesn't hurt, because I think a friendship where you can't be honest is no friendship at all. There may be some awkward feelings and conversations, but make a conscious decision to be there for each other and to try to work through these things together and not apart from one another.
I read in a book somewhere that pregnancy and infertility are both equally all-consuming experiences that affect literally every aspect of your being. So, I think the first step for each friend to recognize this and make a decision to be especially tolerant and forgiving--because you'll both have times when you'll be so caught up in your own experience that you'll hurt or offend. One of the most difficult things for me about my friend becoming pg was that it seemed like pregnancy "stole" her from me--she was so sick, and so tired, and so involved in the physical aspects of pregnancy that we couldn't do lunch, or talk for hours, or all the things we had done before. I felt that not only had I lost "my baby", but I had lost my friend too, and why had I lost her? Because she got to have the very thing I wanted most. I was very angry about that.
When I look back on the survival and subsequent strengthening of that friendship, I realize that it really took two. I'm not sure that if it were only up to me to "cope" that things would have worked out. I had a friend who went out of her way to be committed to our friendship and to continue caring about me. I hope that you will be blessed with that kind of friend.
I don't really have any other advice, but just good wishes. I know how hard this is!