But it needs to be added in believably. I'm not even saying it has to be realistic - it just needs to be credible. We do know human trafficking exists. We do know modern slavery exists. We do know there's a lot of messed up crimes happening even in our "safe", modern countries, whether it's sex slavery or conversion camps or child abuse rings or whatever. So it's not so outrageous that it couldn't at all have been done, but you need to give us something that'll make us go "oh, so that's why it really works".
For example, in Jody Klaire's Above and Beyond novel series there's also a school like this. And while I personally also didn't find it quite believable, it takes more care to explain how people the kids are isolated with no way out, how it can operate due to corruption or blatantly looking away and so on.
But here I'm still only getting a vibe of ... that the author wanted a tragic lesbian romance (but only lesbian because of the circumstances, really) thing and thus casually invented this system but neither thought it through nor really cares about it.