Your best bet is to breathe a lot and take a bit of a "que sera, sera" attitude. As we say in my family "some things are not influenceable" and your DD may be one of them (we have family members like that) She is your DD, if she brings Covid home it's a huge pain in the arse but probably not the end of the world.
Bear in mind that she didn't have to tell you about her boss. A wiser child would have thought "d'you know what, I don't want to get a PCR and I do want to stay here so I'll just keep quiet, what Mum and Dad don't know wont hurt them". She seems to have no inner sense of how the things she says might affect you.
I would stop trying to call her and just stick with the original plan for Tuesday unless she contacts you and asks otherwise.
If she does need to self isolate then either she can notify the university and they'll give her support, or you can just decide to bring her home (if she will come!).
She is refusing to come home as she has work tonight and tomorrow night and is more interested in the money than the well being of her family.
Try not to worry about her motives. It may have more to do with rigidity than anything else - she Had A Plan and family cannot interfere with The Plan.
She's violent with me because she sees me as a push over
Is she by any chance explosive-inflexible?