sleepyhead has mentioned this upthread but surely this should be a HMO and not a joint tenancy.
Is this housing on the university accommodation list?
Each room for students should be rented as a single room, not all lumped together on a joint tenancy. It is a HMO (house of multi-occupation) dodge of extra responsibilities that the landlord should be fulfilling because he/she needs a HMO license.
Taken from CAB website
"What is an HMO?
There is a complex legal definition setting out what an HMO is. However, in general terms, it is a building where more than one household lives and shares facilities.
A single household is where members of the same family live together, including unmarried couples. For example, if you lived with a friend and a couple that is three households"
HMO makes it fair as rooms are usually different sizes and are rented according to their size. Your niece's first port of call needs to be the accommodation officer.
Basically if everyone ran off owing rent on a joint tenancy then one person can be held accountable for everyone. So a house share of 8, 1 person could be liable for all 8 people's rent.
As students, each student should hold a separate tenancy agreement for that one room. A decent landlord would do this. That way if someone drops out of uni but remains in the house, council tax becomes chargeable to the landlord. He can evict just one tenant from their one room and the landlord doesn't lose the income on the other rooms. Harsh, but they are "student" lets. Council tax is exempted for students. So if you stop being a student the landlord gets charged council tax in an HMO.