I tend to agree that while it might feel very tempting to move the cuckoo's stuff out of the room, that is just setting up for the cuckoo to do the same back to DD, or otherwise interfere with DD's stuff.
To me this is not a workable living arrangement. On the other hand, if she needs to go back to uni next week, she may need to move in temporarily.
My suggestion is that DD say to all the housemates, very clearly, that she cannot live long term in an environment where agreements are made (eg to take rooms by means of lottery) and then broken, and that therefore she will be looking to move out as soon as possible, and they need to be looking for somebody else to take her room. She then needs to scout around and hopefully find another flat share - eg where somebody has dropped out of uni. Even if the room she finds in a new place is significantly worse than the current available room, I think she should take it, unless it is absolutely dire. The issue isn't the room, the issue is that one needs to be able to trust one's flatemates to stick to agreements, and that trust has been broken. That is not an environment in which one can live for a year anymore than if one of the flatmates was harressing her.
I realise the issue is that, at least short term, DD could be liable for two amounts of rent. Hopefully there are people out there also looking for a room who won't mind the room available and so that problem will be short term. I also don't know how tight DDs finances are, and whether you can help, but I can't think of anything worse than trying to live in what will inevitably be a toxic environment. This will unquestionably impact her studies, and she needs to get out of there as soon as she possibly can and to the extent you can help her, you should.