Hi L.,
I am so glad to hear that you understand how hard this may be for her. I was in your friend's shoes for over 6 years while everyone around me seemed to have NO issues! I was very upset, jealous, and bitter when it was a woman that would complain about it or in my eyes was a bad parent to begin with.
*Tell her one-on-one so she can digest the information without worrying too much about what other's may see on her face. She will try to hide any pain she does feel, but at least it is with you....and you understand it.
*If you see the look of pain, address it if it feels right by simplying saying "I know you want this too and I feel terrible that it hasn't happened for you." Then drop it if she doesn't say any more.
*NEVER complain about your pregnancy symptoms around her. It can be a slap in the face to someone who wants it so badly.
*Keep her in the loop and be her best friend. I'm assuming she's been around you pregnant 3 other times.
My best friend let me be in the delivery room for her first 2. It allowed me to be a part of something I thought I'd never experience on my own.
Congratulations on your 4th blessing!