Firstly, well done in leaving P1. It's hard the first time, for mums.
It is sad to hear things through Facebook. It is easy to drift apart, and if she wasn't aware of why you drifted away, she won't understand why. She'll probably assume it was just one of those things.
What do you think about contacting her, and asking to meet up once things have settled down with the new baby?
PND has had an effect on you and your friends, and I can understand feeling sad and angry about that, but it is no longer part of your life to the extent it was. You are strong, you are lovely, now is the time to reach out to new friends, and some of your old, one day at a time.
From your online friend, look forward, you will have friendships like that again.
Holiday was lovely but ended less happily. Another story for another day.