I do have some experience of this, I regret to say. Boarding houses can harbour of bullying children and schools do not see what’s in front of them. They absolutely will put money and “premier” parents ahead of mere mortals. These parents are often ones where generations have been to the school or DCs have special talents and thirdly where parents are sufficiently loaded to tap up for big donations. Their DC are more or less walking on water. Occasionally DC know this and push their behaviour to extremes in a show of brinkmanship. Schools rarely deal with them. Instead they wash their hands of what’s going on and are happy enough to let other DC leave.
My DD had lies told about her. She was investigated by the police. It was all based on lies. Did the bullying liar leave? Or get excluded? Of course not. Two of the three criteria for keeping DC were met! She was the most lying, manipulative and awful child I have ever come across but the school didn’t see that. DC who were framed by her were treated very badly.
We hung on for GCSEs. Our problems were in y10. Said bully ran away from school with a boy and couldn’t be found for 2 days. The school was agog! Everyone knew this DC was trouble so, by not dealing with it, the school ended up in real trouble. After the lies were exposed, the one pupil who was permanently excluded as a result of this debacle was reinstated but she didn’t come back.
So, as you can see, there can be dire circumstances with not tackling DC who bully and are manipulative liars. For everyone.
I would strongly suggest your DD doesn’t go near this girls house. She should surround herself with kinder people and I think you look to stay. Only if DC bully is dealt with though. No one will notice what’s happening at parents evening. Yes, you should have left earlier. I know I should have pulled DD earlier. However we had misplaced faith. A change of staff made a huge difference and I know the bully wouldn’t have been believed or even admitted to the school under the previous HT. Money and status spoke though.
Don’t stay for A levels. Your trust has gone. Other schools will be better snd friendly. You cannot “file charges”. It’s not the USA. We have the CPS and they decide. Not you! So negotiate safety for your DD. She won’t have finished teaching and learning. Don’t rush to leave without being absolutely certain she can complete the exams. She may well be compromising results by going elsewhere.