Yes, one can always "hope" and maybe they just didn't realize how monopolizing they were being and will be more considerate next time...I just wouldn't count on it, LOL!!
Sounds like you and your daughter have a wonderful relationship, and her seeing the MIL ways, she probably appreciates you even more! I know I do with my mom, I didn't realize what a gift she gives me by not always offering advice unless I ask for it, or always telling me the "best" way to do things. When you have a great example and a not so great example, your come to appreciate the great one...I know how to be a good MIL (long time from now hopefully) just by seeing the way my mom is and the way my MIL is!! Anyhow, I wouldn't let her monopolize those grandkids, just get in there and grandma away!!
