Actually, in my humble opinion, you need to do more of this- what you did. Instead of bailing her out, continue to focus on you and DD. She's made her bed, she can lie in it. Sure, she's your D's mom- and anything that concerns D- XW can't pick her up, D can't be with her b/c XW is really sick, etc., of course you'll come through. But if she doesn't ask, do not step in SR. You still need major detaching- b/c you're even considering swooping in to help still.
Re-read what you wrote above about what she said. This is how she thinks of you: a convenient money source who bails her out and that she's entitled to your help. Unfortunately, she probably would not feel the same as you did if she heard you were sick- I'm sorry, but given what I know, that's true.
Someone here said something like (maybe robx?): Never make them the priority when you're the option. Every time you do, it chips away at a bit of yourself until all your behavior, actions, thoughts revolve around this person who has many other options, with you being just one of those options that's sometimes convenient for them to lean on or get help from (think of all the times: she needs $, her roommate is leaving, she has no childcare, is without her furniture, she needs your help with the DSL, etc. And think about how she's sweet right before she needs something from you... But during all the other times- 99% of the time- does she act kindly? ask about you? even act as a friend? I'll leave you to answer).
As your friend, I want for you what you want for me- to focus on you and DD, be the best dad and happiest person- independent of STBXW- that you can be. As time passes and you work on this, you will naturally act on these "save her" thoughts less and less, then feel the need to write about them less and less, then THINK about them less and less, until, one day, a few hours or days will pass without you thinking of her in any capacity except as a co-parent. It will happen, but there's still a lot of work to do towards it. You don't have to forget the good times or hate her, you don't have to be mean or vindictive, but you also don't let her win by letting your anger and hurt keep you stuck in limbo or some dark place, or even let her take up any more than the minimum space in your mind while you could be moving towards a better future.
((((Big Hugs))))
-A
When the men on the chessboard Get up and tell you where to go; And you've just had some kind of mushroom And your mind is moving slow; Go ask Alice... I think she'll know.