I have gone thru this situation numerous times over the past 8 years... all I can say is it's very hard.. but I have really tried not to put my problems onto other people. It's not their fault I can't get pg, so why should I make them feel bad. I've never kept away from any friends or not talked to them about it, but I've really appreciated it when they've been sensitive to my needs as well.
I would say that means not moaning about getting fat, or sleep deprivation, things like that. Sometimes, tbh, you can't win... if she's feeling fragile running up to AF or CD1/2, which are my worst times, I just distance myself at those times a bit.
One friend I had, I supported thru both her pregnancies. She conceived both her children in the time I was trying for my first, she lived in Scotland and if ever there was someone I could have avoided it would have been her, due to the distance, but no.. I used to go up and see her at all stages in her pregnancy. When my IVF failed 1 week before her 2nd was due, she got funny with me because I was distraught and said couldn't be like I normally am, cooing on the phone at every detail. Needless to say, she's not a friend any more.
I'd say you're a pretty good friend for even bothering to find out how to act. If I were you, I'd have a good old chat with her and ask her how she wants to play it. I'm sure she'll appreciate that.
HTH.