AITAH for calling the guards on my younger sister?

So for some context i’ve a buddy who works as a guardai and he’s not known by my family, i’ve probably mentioned him a few times but they haven’t met him. I’m 20, I’ve two younger sisters who are non identical twins aged 15 and an older sister who’s 30 (not living with us).

One of my younger sisters who i’ll just call Faye for privacy reasons is trouble, like TROUBLE. Now i’ve always assumed she’s got adhd like me or smth but there’s definitely anger issues mixed in with that. She gets angry quickly and she’ll take it out on who ever is closest with the sharpest or heaviest item she can find. The truth is this kid is strong and fast too. She threw a vase at the back of my head three years ago and i still have the scars.

A couple weeks ago she started getting SUPER pissed off. Constantly having fits, throwing stuff, slamming doors, all that shit. My parents can’t deal with her, my mum will make her worse by acting calm or belittling her, my dad will just act like it’s all a joke which makes my sis even more angry.

I decided she needed a wake up call and a big one too before she gets worse as she ages. So as i was talking to my buddy one night he suggested he dresses up in uniform and knocks at my door asking to speak to Faye about her abuse to the family. At first i laughed it off but then it stuck so a few days later I called him up and agreed. I talked to my parents about it and they seemed fine with it. The next day when they went to work and my siblings were just home from school there was a knock on the door.

I didn’t open it, i waited it out till faith started screaming for someone to get it while she was in the room right next to the front door. After some back and forth and continued knocking she opened the door and there stood by friend Jamie.

He came in giving Faye the whole talk about how it’s illegal to abuse anyone let alone family members, she looked at me for support but i turned a blind eye. He continued to list the laws she has broken trying to scare her out of it. He stayed for more than an hour, half of that time faye cried. Then, he left.

Since then Faye hasn’t caused anyone abuse, when she gets angry she goes to her room, she doesn’t yell at my parents or her other siblings, she doesn’t throw stuff or try cut us with knives.

Honestly I see this as a good thing but when i told my relatives they freaked out saying i’m a horrible older sibling, AITAH?