S.V.
As busy parents, we often only see our family's needs and that's our focus. It's not necessarily right, but it's a survival thing. And not everyone approaches things or handles things the same way. What you see as a problem, she may see as a necessary adjustment in her life.
When my friends and I started having children, we tried to keep the friendship on the same path. There was no way that could happen, but we did the best we could. That has often meant not seeing or talking to each other for days or even weeks at a time. While we've never openly discussed it, we've all reached the conclusion that this is just our lives right now and we will do what we can to be there for each other. We don't get together often, even 1 on 1, but we try to answer each others' calls as soon as possible.
We all need at least one friend that we can turn to when we are down. But that doesn't mean your friends should be available when you want to get out of the house (unless you are planning it rather than spur of the moment).
You might need to have a straight (but gentle) conversation with your friend to tell her how you feel. Maybe she can't handle taking on any more stress or obligations. That doesn't mean she doesn't value the friendship. It is possible that she is just being selfish, but having a conversation with her will help you understand what's going on.
Good luck.