Ok, thanks to all of you for your responses. I have been really thinking about this and why it bothered me so much and why she acted the way she did.
First off, it hurt dd's feelings. She told everyone that she had to be at the field at 5 and she felt like it didn't matter to anyone as long as everyone else got where they needed to be. I told her that wasn't the case, it was just a lot of mishaps. Her grandmother passing it off as a joke didn't help her feelings but there wasn't much I could say to that, except "grandma didn't mean it that way".
Secondly, it does bother me that she treats dd's activities as completely unimportant. It wasn't that way at all when my sons were young. Its kind of hurtful that their baseball games were this big family affair (me, dh, my mom and dad and both sons going to every game), now the only one going to dd's games is me (dh is out of town all week) and sometimes one ds, the other ds, that played ball, is texting me throughout the games, lol. But, I do understand why it is that way.
My sister was just the innocent bystander. She had already told her dd that she would get the dgks to their appointed places when mom called and let her know that she was going to town and needed sis to take my dd with her.
Now on to what I plan to do about it. I am making arrangements at work to pick dd up from school on game days. And my sister and I are working things out for the other days. I am in the process of making sure the summer is covered with church camp, softball camp and show choir camp and my mil (who has asked for dd to come stay a week or two)
I love my mom but this just isn't worth the stress.
Thanks to everyone. I just needed to hear (read) what I already knew to be the better solution. I still am unhappy with what she did, but I cannot let her reasons for doing what she did to continue to bother me.
I jsut think it boils down to common courtesy and she didn't show me that.