Do you agree that there are different friends for different times of your life?

I have a friend who had a baby last June. Since then, she has been a little MIA. It's totally understandable as she is focused on the baby, her husband and career. In January, I texted her (since she doesn't answer phone calls) and said "Just thinking of you. You've been MIA." She replies "Not MIA, life is just crazy right now!" Now that she joined Facebook, I can see that her social life has not stopped and now she has new "mommy" friends. I held her hand through bad relationships, borderline divorce, family issues, etc. Now, it feels that I no longer fit her new life.