Hiya Hops:
Finally got a chance to read this whole thread and first, I want to acknowledge your feelings and say that when people close to us say or act insensitively, selfishly even, it seems normal to feel sad and hurt and not cared about. So your feelings seem pretty normal to me. So sorry for that pain, Hops.
A couple things struck me though, reading back on page 2, I think:
I used to refer to my D as "evidence of the god of getting one thing right." To see what we are now, I guess, feels like "evidence that I really have not done anything right." Anything that matters, anyway.
I do this to myself too Hoppy. Ha! When everything's perfect.....it's out of my hands but when stuff goes wrong.....it's gotta be my fault....right?

People make choices. Your daughter makes them just like the rest of us. Much of what she chooses has nothing to do with you. She's an adult who is capable of behaving well because I bet my bottom dollar you taught her how to behave well...??? Therefore, when she gets grouchy and inconsiderate, is it God's doing or your doing or her doing??????
I think maybe she chooses and because she's human and fallible.....she doesn't always choose wisely. Not your fault. Not God's fault either eh?
So lift that weight off your shoulders and give you a break Hops.
Also, what you said about your D enjoying it so much when it was just the two of you struck a nerve in me too because I remember a similar time and know my kids want me to themselves and will do anything to get that. Maybe it's a normal longing they have after having that experience. AFter all, can we blame them?
And now that they're grown up.......we are still mothers. You will always be a mother (and a wonderful mother at that Hops!) no matter how old your D gets. Maybe children are always children, in a way too, and will always act out where they feel most safe?? Maybe they will always be less mature around the one parent they feel will love them regardless? I don't know. I was just thinking out loud there.
Also, you taking care of your mother might be something she doesn't think she'll be able to do? Maybe she resents you doing it because she doesn't think she will want to or be able to? Ofcourse, she really doesn't know how she will feel or what she is capable of until the time comes and things could be much different by then eh? But now, at this young age, maybe all she can see is you.....wasting your life.....being some kind of martyr......as her grandmother acts thankless and even nasty (in her view)? Maybe she criticizes because she cares and wants you to be free from all of that? And maybe a little selfish wanting you to herself to boot? 'Cause around you...she's still a kid?
Last thing Hops: Please don't allow yourself to feel responsible for so much. You aren't. You did all you can do (back on page one, you said something to that effect.......yep! I agree!!) and you are longing for an adult relationship, which is reasonable. The thing is....maybe she's just not mature enough yet for that? It may still happen Hops. Maybe for awhile yet, you just have to be the grown up, until she grows up a little bit more? She's an adult but not a fully mature one yet maybe?
(((((Hops)))))
Sela