Are we sure that all the house girls were forced to work at the carnation club? Kimber was desperate that her shifts would be cut, Dahlia and Harper had been in business for more than 10 years, Andrea was on loan, and some of the girls even got pregnant at work.
The club is a terrible place, of course, but it's unlikely that EVERYONE is there against their will. I mean, all carnations participate in the exhibition voluntarily (technically). It would be very ironic (in a bad way) if the house girls could eventually leave the club, but the carnations would remain on the hook even after the exhibition , like Alisson
Forced is a tricky word in the context of this game. AFAWK, the house girls - just like the Carnations - are working voluntarily; they can theoretically quit at any time.
The issue is that there's a reason they are working there in the first place. For some (like Andrea), it may just be a job that pays well and has good perks so there's no reason to quit. But for others (Nicolette most clearly), working at the Club is evidently a way to settle existing debts, so quitting early would have dire consequences even if said consequences didn't come directly from the Club itself. I suspect that there are more girls in the latter camp than the former, and you could argue they are being "forced" in a loose sense of the word. But even they can eventually leave if they pay off their debt, and I definitely don't think
all of them are forced, even in the loose sense.
IMHO, Allison is a bit of a special case. She's effectively in the former camp, but she's more of a freelancer since she has a lot of options open to her if she wanted to walk away. However, turning down ongoing 'offers' from the Club not only runs the risk of terminating her new career early, it will also deny her potentially lucrative options in the future, too. So I suspect she's relatively willing to answer Kathleen's summons in return for suitable compensation.