Hi,
I am guilty of this.. I'm a mother of 2, and my social life has changed dramatically after I have my first child. I noticed most of my attentions were toward my babies, and my friends who I care so much slowly dissapearing. We used to hang out all the time, shopping together, lunch, dinner, bars, parties, travel, and do all sort of things that we could possibly think of.
I know friendship and social life were important to me, but I know my children and my family is THE most important subject in my life right now and will be continue to be my first priority in my life. One of my best friends once told me "it is hard to hang out with you now, because you always have to bring your daughter out wherever we go.. a stroller, smoke-free restaurant, child-friendly environment, that's why I haven't called you".. It broke my heart to hear that, but I do understand where she came from. I also "thanks" her for telling me how she feels about my "status" change as a "mother". Sometimes, I feel jealous for my singles/non-married friends that are able to go out and have fun without curfew and responsibilities.
It was hard in the beginning, but slowly, friends that are true to me are still around and are still able to spend lots of time shopping, doing nails, hit the spa or even go on vacations together. These friends are not necessary are married and have kids to be able to share fun with... They are singles, some have long term relationships, and some are also married. A few of my un-married friends always tell me how lucky I am to have a loving husband and 2 wonderful kids. Sometimes, they even tell me how jealous they are of me.
I think grass is always seem greener on the other side. But, I am no longer envy my singles/unmarried friends.. I just accept them as FRIENDS whom I truly love and care and appreciated. Being said that, still I try to make time and hang out with them whenever I can, but if I am too occupied with my kids, they DO understand. Good friends will be there no matter what.
You should understand life status changing is a big deal for your friends with babies now, and they do need your support and understanding. Tell her how you feel, and I am sure she will appreciate your honesty.... Hmm... I think I am speaking for your friend now...

hope this help!