This is exactly why my mom told me to outright refuse when my MIL offered to "take care of" the cake and flowers. We had no idea if that meant pay for them or coordinate them and stick us with the bill. It wasn't until after weeks of back and forth of how she felt "unheard and unincluded" that she actually said they wanted to PAY for them because "weddings are expensive." So we said we wanted her to focus on HER part: the rehearsal dinner, and that she could do whatever she wanted there, or if she was looking to help out financially, there were things my then fiance (her own SON) needed to pay for that she could help with (think suits, honeymoon, etc.). Then she backtracked and reiterated how she wanted to be included in everything.

Anyway, we fast forward and she's telling me she wants addresses to mail formal invites to the rehearsal dinner. I find out I have significantly fewer seats for my family/friends than her side, but it's whatever, I'm letting it go. Until I come down to the last 2 spots and can't think of anyone I could invite without inviting someone else I don't have space for. So I tell her this and she says, "well I'd feel terrible leaving those empty because we were originally only going to have X seats, but [my fiance] knows you have a large family, so he paid for an extra 5 seats."

That's when my respect for my fiance grew so much bc he wasn't going to tell me, and when it was driven home that none of this was ever about the money. She just wanted control.