I need help with my mom and her obsession with spoiling my sister's dog, any advice?

[AmeeliahLeh]

I really need help with this, just yesterday she was screaming about me not letting my sister's dog have his way then denying the fact that she just said that she wanted it that way. She said some stuff like "If he wants more food or "human" treats give it to him cause his owner (A. K. A my grandpa, A. K. A her EX Boyfriend/husband thing-) died and they need royalty!!! but my late rabbit was passed around and then given to us and she wasn't saying anything like that. Honestly, Our rabbit's diet was all over the place but he was healthy some how XD we literally gave him all the bad stuff and human food in the book (Except meat even though he got to it a few times, No, if you're wondering he died of old age not of poison)
but anyways, Like, do you want him to be obese cause you're literally encouraging the behavior, She treats them better than us honestly. She ask as if the dogs we have are little angels who can't do no wrong but c'mon! nobody likes a dog thinking that everything is for them, no. This would've been easy to handle if I were in control but miss girl is and she keeps giving them what the heck they want and this is why their personality just gets more worse. I really need help, please don't make any "Oh but you can just stand up to her" no, she is one of those people who tends to put their hands on you and assume stupid stuff if you prove them wrong. before you ask yes, she is an emotional/physical abusing narcissist. but I really need advice.

[Guy13]

Mom and Prt Psychologist