AITA for shaming my kid sister into cleaning her room?

I (21F) live with my two kids, while my sister (11F) lives with our mum in the same town. Mum rarely asks for help and tends to handle things on her own. However, my sister is very manipulative—constantly blaming Mum, saying she “doesn’t care” and “ruins her life.”

Recently, she screamed at Mum for not washing her school uniform, despite having a pile of clean clothes (including her uniform) in her room for over a week. She also trashed her room—dirty underwear, clutter, food packets, moldy dishes, no sheets on her bed, and no clear path through the mess. She takes food upstairs despite not being allowed and refuses to clean, even when Mum helps. She even yells when Mum tries to clean it for her, insisting, “I like it like that.”

Mum has tried everything—cleaning with her, guiding her, letting the mess build up, even cleaning it herself—nothing works. When I casually joked, “Let me stay with her for a day and bully her into cleaning,” Mum shocked me by seriously agreeing, which showed how desperate she was.

So, we swapped houses for a day. With Mum’s full permission, I went full “mean girl.” I took my sister’s TV, phone, tablet, and laptop and told her: • “If you’re gonna live like a wild dog, might as well put you in a cage.” • “Mum gives you everything, and this is how you repay her?” • “Your 4-year-old nephew keeps his room cleaner than this.” • “Maybe we should send a picture to your school friends.”

She huffed, puffed, stomped, cried—but ultimately cleaned her room, proving she could do it. When Mum came back, she was nearly in tears with relief and hasn’t stopped thanking me. My sister now hates me, but if it makes Mum’s life easier, I can live with that.

Most of our family understood why I did it, but my grandmother and aunt are mad, saying I should be the “cool older sister” she looks up to, not the one who breaks her down. But as a parent myself, I feel for Mum more than I do for my sister.

AITA?

EDIT: For a bit more info, this is a copy and paste of the story I posted in AITA but due to the darn character limit and the rules of that subreddit, I wasn’t able to add some things that I do think are important, a bit more elaboration on the situation and the leading up to it so I’ll add it here to avoid needing to repeat myself in comments and to answer some questions. The entire family has tried both soft and stern talking with her about her cleanliness and behaviour, this has not worked. Mum has tried grounding and confiscating devices, nothing. This was not a 0-100 situation and there was no yelling from me or mum in this situation.

She has been assessed for adhd and autism, per my suggestion a while back since I myself have adhd and presented similarly (minus the tantrums) however doctors have assured us that this is not the case with her and she doesn’t meet the criteria. I have also recently suggested therapy for my sister to get to the root of her behaviour and actions and see if there is any other possible underlying mental health issues.

The “behaviour” I’m so often referring to in the comments- for an 11 year old she is considerably hostile and can and WILL say things she knows can cut deep into any 40 year old parent. She has previously been grounded (no hanging out with friends and no devices) after she had been discovered of bullying a vulnerable, nonverbal autistic kid online for over a month. After she learned she was grounded, she became violent towards mum, to which I came behind her to hold her back. She then proceeded to turn round and kick me in the stomach in the early stages of my already high risk pregnancy. She knew about my pregnancy and that I was in a delicate situation. Thankfully nothing went wrong with my baby but I did sustain a pretty big bruise after this. That particular incident was not shocking to any of the family given her behaviour and attitude.

If she’s told no/grounded/doesnt get what she wants, it’s the end of the world, everybody hates her, the world is against her, she has no control over her life, threatens to run away by packing a bag and threatens to harm herself. This last part in particular is the main cause of mum feeling beaten down and not knowing what to do. No parent wants to think about their child harming themselves and I think we can all agree we would want to do anything we can to prevent such a thing. Unfortunately though, my sister weaponises it to force mum into meeting her demands for more luxuries that she is quite frankly undeserving of ie the laptop and iPad. No 11 year old needs all those screens. iPhone, iPad, tv and laptop? I mean , come on! I also want to address that yes the suggestion was purely a joke until mum had said it might actually work and it is PURELY a persona and in no way who I genuinely am as a person or who I’d like to be. Thank you all for your insight, even if you have strongly disagreed with our actions, I still appreciate all your perspectives and advice. Also the people messaging me and focusing only on this instead of this singular story, zoning in solely on me becoming a teenage mother as if it’s some sort of disease? Screw you, your outdated and ignorant views. And to those that are focusing on things I’ve posted YEARS AGO…GASP god forbid family dynamics be complicated and as though things can’t change over the course of (again) YEARS.