Oh there are a few deadbeat moms I know of.
One of my ex-colleagues is one, sad to say. She goes clubbing and brings different men home on different nights. One time I had to send over something to her place and I caught her cajoling with this guy that looked like a complete ass WITH BOTH her sons in the same room. I was so mad! Poor kids. They must have been so confused. Mom and dad share custody, but their dad is just like their mom, if not worse. I don't know, I just feel very disappointed when I see such things happening. Last I heard the kids are staying with their grandparents permanently, which I think is better than getting kicked around here and there like an unwanted ball.
I think you just have to be blunt and firm with your friend. Tell her straight up what she's doing is bothering you. You have to stop being a pushover at some point.
Good luck and god bless you for being such a kind soul.