How about "As we discussed, I would like to take the kids to reunion Staurday. I'll pick them up at such and such a time. There's a hockey game after might get a hotel room with kids. I'll let you know."
Leave out the part about she isn't missing anything and the invite.
I wouldn't add Mom sends her love either. If your mom wants to tell her that, I'm sure she knows how to reach her.
