oh, rickman, I've been there too! When I was pregnant and stressed, a woman popped into my life and became a close friend, did the whole lot - visiting at hospital, running me around in her car as I couldn't drive then, telling me nothing was too much trouble. Soon after my son was born she lost all interest. I definitely think she needed to be needed and liked the drama of it all. Her mother became ill soon after, I offered support in return, but she said she was too busy to see me. We sort of lost contact. It ended with her refusing to give back some good furniture dh and I had lent her for her new house. She said she had sold it on. Very odd. Wierdest of all, a year or two later, when I bomped into her at a party, she was friendly again, picking up where we had left off.
Before children, years ago, I can think of a another friend who did this too - my partner and I had fallen out and I was upset. She was wonderful in supporting me, telling me all men are B**DS, etc etc. She disappeared off the scene as soon as I made it up with my partner and planned to marry him.
I think some people keep repeating this patten with their relationships - they give all, feed off the drama, then feel put upon, then say they were used. I don't know why this is.
This woman you know might have lots of friends, but I wonder how long they have been in her life? With the women I knew, their friends were mostly recent ones (one or tow years at most). They were excellent at making friends but didn't keep them long.
I don't think there is anything you can do, tbh. You have done all you can to communicate with this woman. The chances are other people know she is wierd with friendships, so if she does say anything about your, will take it with a pinch of salt.