You need to address this toxic friendship - she's bullying your daughter while pretending to be her friend, and your daughter seems to understand this, as she says that when her friend joins in activities your DD has started, that she spoils them. She isolates your DD from other possible friends, she won't even let your DD sit beside her in a group, and then she's being spiteful and wrecking your DDs room. She's not your daughter's friend, your DD is her victim.
I think you need to talk to the school and let them know whats happening, so they can split the girls up as far as possible - different groups in PE, not doing projects together etc. They'll have seen it before.
I think you should talk to the friend's mum, and let her know that you want your DD to make somr new friends, so you think it would be best if her DD doesn't do whatever class/hobby your DD is going to join. Probably no point in telling her how her DD has been behaving, she may not accept it.
You need to support your DD to grow away from this girl, or your DD could easily end up in a more abusive relationship with a boy, as she's learning from her friend that's her feelings aren't important, and that a toxic friendship is better than nothing.
I suggest scouts for your DD, they've well run, inclusive, build self-confidenve, and the kids who go tend to be nice.