For all anyone cares girlfriend could be a lodger, a relative, a live in nanny. As long as she becomes part of that household for the month, she is allowed to be there. She just cannot go to and from another household.
Fwiw, none of my kids have been home since beginning of term and not have I visited, except once to drop off groceries to fresher ds2. Ds1 was in a v fragile state with a UTI /needing groceries /disorganised and had every reason to be visited, but I still didnt. Ds2 is fine.
As far as I can make out the rules on households aren't going to change, and everyone with a bf gf they don't and cannot live with, is going to either have to accept Draconian restrictions or use the rules to fit their personal circs.
Nuff said.