I've 5 kids. 4 of them have been 12. Mix of boys and girls. TBH it is her age. I found they were all like this. The girls at around 14/15 snapped out of it , the boys around 15/16 snapped out of it.
I did spend about 2 years on my eldest a boy, nearly crying for him to wash, pick up clothes, clean room etc I was using every punishment in the book. Nothing worked.
My second a girl, I thought this would be different, but it was worse, they have more bits and pieces, so bedroom was like a bomb went off. The attitude was worse, the back talking was worse. Again I tried every punishment, nothing worked, she really rebelled.
Then they hit the 15 year's, well...... it was like I got new kids. Don't get me wrong we still had the bit of attitude , rolling the eyes etc but they couldn't wash themselves enough, then taking care of skin and teeth, they took such an interest in themselves.
They both looked after their rooms, they liked having friends over and liked it clean and tidy, there were a couple of hic ups but nothing major.
My next 2 when they reached 12, same shit again, only this time I didn't waste time arguing or getting upset, I did still point out that if they liked living in a pig sty smelling of sweat that was their choice. Again once the 15 years came, big changes in them.
So personally having taken away privileges and leaving them had the same result. I did keep speaking to them on cleanliness etc it's definitely the age, everyone goes through it, keep your own sanity and have a chat explain about smells etc it doesn't matter how many material goods they have, they never really show appreciation, they'll thank you and love them and will be delighted to have them but they certainly won't be bothered having them removed, they'll find something else to distract themselves, which is usually something more annoying.
Every year there is a 'phase' for kids. I do think the 12-18 is the worst 🙄 the only thing is you get a bit of variety throughout these years. You wonder every morning who's going to come out of the room.