That last strip tends to indicate why Elly lets people walk all over her so often. Somewhere along the way, she seems to have come to the conclusion that people only noticed that she did things when she didn't do them. We can see the general logic that makes her come to this conclusion by focusing on why Michael does things he doesn't want to; instead of being motivated by any sort of pride in a job well done, both he and Elly do things to avoid censure. (Also, both of them are all too eager to please people who do not have their best interests at heart but I'm not going to go into that today.) What this means is that Elly would rather wear herself into a frazzle pleasing people who don't really care than do something that makes herself feel good. People get like that when they can't let themselves be happy.
The thing that makes her an almost-sympathetic figure is that she doesn't actually realize that she does this to herself. She might think that she's a bastion of firmness who isn't influenced by people who live to take advantage of her but her exploiters know her better than she knows herself. What prevents me from feeling too bad for her is that her lack of self-awareness also extends to her very strong need to be thought of as somehow being inexpendable. I'll flog THAT dead horse tomorrow.