Eternal Love does not have the ability to influence her SIL in that matter unless she is prepared to move out. She is not because she has not yet saved up enough money. The whole family is used to outbursts and expect her to not pay attention to them similarly to how they themselves ignore them. The SIL's expectation (and rule) is that bonding over food happens among people other than her husband and despite anything her husband does or says. It may seem unfair but it is what it is. It is not a bendable rule. She is very clear about it.