Avid CFer here, and yes, that really is "just how it is." Your life is different now--and congratulations on your new DD!
There's something terribly wrong with new parents who are eager to dump the baby on Grandma and go out clubbing with their childless friends just a few months after the baby is born. Your child *is* the most important thing in your life now--which means you're a normal healthy new mom.
Your life has
changed; it is
different now. And vive la difference! You have a wonderful new priority in your life, you're taking on new challenges and new experiences, and you have a chance to make new friends with similar priorities (mommies group, day care, etc.). Your clubbing friend would be bored to tears with hearing about your new DD's sleeping schedule and feeding schedule; and you'd probably be bored to tears hearing about her shopping excursions, dates, office intrigues or whatever when your heart and mind are with your new DD.
Let the friendship drift for now. She's not really trying to understand your life right now, so she's not really being a good friend, despite what she says. You're
being a good parent by understanding that you can't take a newborn (or a hyper toddler) to French Laundry for a three-hour $200 dinner, or spend all day with her in the spa while you're still BFing.
I may be a CFer but I'm supportive of my friends who have children. Heck, I even babysit. A good friend understands when priorities change, and celebrates your joys with you as well as holds your hand during your sorrows. (Did she even send you a card or call and say congratulations on your new arrival?) A good friend doesn't
say "Ditch the kid and let's go paaartay!"