I think the biggest issue that we all deal with as we mature into adulthood is realizing what incredibly selfish assholes our parents actually were all along. lolI agree. I usually offer my parents money to watch my kids even though they don't need it, and say thank you every time. Maybe tell her that if she "doesn't know" when she's picking up her kid, tell her that you "don't know" the next time you'll be able to watch her.
P.S. My parents didn't go to my son's school Christmas concert because they went to the casino. I know I asked kind of short notice, like a few days before, but seriously?