Just implement old faithful and nickname your significant other Bambi! They should assume its related to their (hopefully) “big” brown eyes yet it will provide some comic relief as you’ll know its only cause you want to kill their Mom lol. Extra points if you can overtime have your MIL call your significant other Bambi too.

All joking aside, have you talked about this with your partner? They should be able to offer some insight regarding how to best correct or smooth out the problem I’d bet.

My MIL is pretty chill NGL

Not a all, we get along quite well.

I’m not sure if they count as a mother in law, because not only is she not really a mother figure, but yeah.