K.R.
whoo.
Before I get to the "yes you're right," I'm gonna say the one thing you are wrong about: you *are* expecting too much if you expect her to prioritize you or be there for you. Not because a daughter shouldn't expect that of her mother, but because clearly that is just NEVER going to happen for you. I'm really really sorry about that, but probably you will resent things less and open your mind to alternative answers and resources if you just admit that and let it go. (One of my proverbs to live by: Reality is that which does not change, no matter how much we want it to.)
But otherwise, you are crazy-right, she is ridiculous.
When I was dealing with my divorce negotiations, not only did all the books speak very clearly about how everything for both partners, no matter how angry anyone was, should be 100% (as much as each partner is capable of) About What Is Best For the Child(ren) ... but someone phrased it for me this way: I had to do as well as I could in the negotiation process, because I was defining a large part of the next 18 years for myself and the children.
What you choose to do, and the lines you choose to draw, WILL PROTECT YOUR CHILDREN (or won't!).
And a woman who has consistently chosen THAT poorly, will continue to do so unless she has made some radical changes ('sounds like she hasn't). The title of your query really suggests the deeper problem, which is protecting your daughter from abusers she would be taught (by Grandma) to trust.
Another piece of divorce-book advice that is very pertinent, is that the parental-type adults in a child's life should not even *introduce* the idea of a romantic partner until and unless that relationship is long term and looking stable. There are all sorts of scholarly and plain-speak explanations for the damage this *is guaranteed to do* to the child(ren) involved if their grownups ignore it ... perhaps having several 'relationship' books draw her the same line you are trying to draw might at least get her to stop blaming you for her issues. (Probably not, of course ... but it's worth a try, and you might feel better supported in your choice.)
I am so sorry your mom is so dysfunctional. When things began to really fall apart between my husband and I, I had to make a conscious effort to open up and move out into other "lesser" relationships for my support--letting go of my "ideal" (main support will be husband). It really feels like this is the same motion you maybe need to make now: she won't move with you to a healthier place, but you don't have to be trapped in her unhealthy one. You can move forward without her, and her judgments (condemnation or approval, neither are probably a good idea for you). Painful as it is, just let her go. Part of the reason things fell apart in my marriage is because I was making healthier choices (*hard* choices, growing choices) ... and even when it meant losing him, I would not renege on those decisions. I just wish he had trusted me and come along too ...
: (. It is a sad thing.