It sounds like Mom is making zero effort to meet you part-way, sniping even when you make obvious concessions to her. If she's going to blow up anyway, the timing and setting may as well be under your control.
Perhaps your SIL could say something to Mom in advance like "in my house we're following my rules, and that means he's wearing Glenn clothes", to sort of prime her?
an outsider's perspective
Perhaps your SIL could say something to Mom in advance like "in my house we're following my rules, and that means he's wearing Glenn clothes", to sort of prime her?
Good luck! *hugs*