First of all, I remember feeling very insulted when people with kids asked my husband and me when we were gonna "start a family". We'd already started, just by being together ourselves. What if we'd never had our own baby? Would we not be a family? Please try not to think of her in those terms.
Anyway, maybe she's jealous and doesn't know how to deal with it. Maybe she is not so sure how to relate to you anymore. Maybe she doesn't like this new "mommy" you and wants to keep the you she's familiar and comfortable with. I had a friend who bled my same blood. When I got married, she kinda pulled away a little, but we were still very close and interacted regularly. When I bought my house, she kinda turned on me. I showed her pictures and was all excited, and she just kicked me with negativity. I told her that it bothered me when she did this and when she had less time for me while making more time for other friends, some even married. One of her big problems with me is that I always make a point of seeing the positive and trying to get over stuff. She thought that I was too much of a goody-good. Huh? (I forgave her for something very hurtful that I found out about years after it happened, and she was annoyed.) Anyway....
I say all that to say that you need to look at your dynamic and realize that it's different now. She has a right to feel however she feels about it, but you can't know her feelings and work through it all with her unless you are willing to talk with her openly about it. Be prepared to get your feelings hurt and maybe to hurt hers. You'll walk away with a different relationship.