I suppose there is likely to be a "boss" around who rents the flats, finds the girls and then rents the rooms on to them at inflated prices. That's how most foreign girls will be working I'm sure. But forcing a girl to work, in this particular flat, seems unlikely. Bianca recently went to Romania for 3 weeks holiday and as I said, seems cheerful and in control.
I think you have hit the nail on the head there, regarding set up of how this business works in some cases,( after 4 years punting on and off ) getting to know a couple of escorts etc as regulars and piecing things together,this seems to be quite common rent a 3-4 bedroom house / flat advertise in local newspaper at home,get the girls over here and charge x amount of £'s for one room per day, electricity etc.