Bratty sister in law

My boyfriend & i live with my mother in law.

He has a brother & a sister younger than him.

His brothers 21 & his sister is 17. I get along with both of them but his sister can be such a brat at times. Not with me but with her parents. I understand as a older brother my boyfriend is going to make sure his sister isn’t making wrong decisions. I don’t want to get in between cause i feel like that’s none of my business.

There’s times that she’s out with her boyfriend & her mom & my boyfriend tell her to be home by 10:30 or 11 the latest. But she gets home until 2am. What bothers me is that my mother in law is calling her & she tells my boyfriend to call her & to go pick her up from her boyfriends house. But then when he does he starts to get frustrated because she turns off her phone & doesn’t pick anyone’s call up. & so when she does get home my boyfriend is trying to talk to her & tell her what she’s doing is not right BUT there goes my mother in law telling him that he shouldn’t say anything to her & to leave her alone 😒 Which annoys me because first she wants him to call her & see where she’s at but then gets mad at him for telling her that what she’s doing is wrong ( Staying at her boyfriends house til 2 in the morning)

Also she might graduate this year, & the only reason i say might is because she’s missing some credits & she’s always missing school ( Even tho we literally live right next to the school )

so the school is always calling the house saying she’s missing school.

Well today while i was making dinner she was in the living room with my father in law ( Keep this in mind he recently got his foot amputated)

So he told her to clean her room & she started getting an attitude & he told her that she needs to straighten up because the attitude she gets with him is not okay.

So she just laughed it off & he told her that if the school calls one more time he’s personally going to go to the school & tell them to keep her from graduating if it’s necessary.

She literally bursted our laughing in his face & told him “You? You’re going to the school, how? Did you forget you have no foot”

i just stayed schocked. i literally wanted to cuss her the fuck out of her! Getting his foot amputated really hit my father in law hard it got him into depression also & for her to say that really annoyed me.

There’s other times that i just want to tell her off but then i think about it & i don’t think it’s my place to even say anything.