If it were me, I would honestly try to organize an extended face-to-face interaction with her to talk about what problems she has with you. But my personality is very confrontationalist. I tend to get in people's faces if I believe they have unjustly done me wrong.

But I think the fact you mention your mother has been married and divorced three times is significant. Have your other siblings, the ones she speaks highly of, likewise been married/divorced multiple times, as you have (married, divorced, then married)?

You say you couldn't figure out why she wasn't more sympathetic after you divorced your first husband and became a single parent. In my experience, humans are naturally hypocritical creatures. Perhaps she was ashamed of you not fixing her mistakes (living one happy marriage)? I think parents tend to do that a lot - expect their children to right their wrongs. Perhaps it is what your mother was doing to some extent.

But anyway, the best advice I can give is something that may or may not work for you. For me, I would absolutely confront her and organize a face-to-face talk and attempt to get it all out of her, to lay the cards on the table and find out what you're dealing with. It's not a marriage, of course, but if your mother is holding some unhealthy emotions deep within her, they can be attempted to be unearthed in a manner similar to dealing with problems couples deal with in marital relationships.