Good for them mammy. I don't personally care if someone wants to choose to be a prostitute (which is what I personally think cam work is).
The issue here is this particular woman isn't making enough money to pay her rent (or she is but she's choosing to spend it on other things, like going out with her mates, whilst trying to manipulate/guilt her mother into paying it).
She is expecting her mother to pay her rent, despite the fact she's a university graduate in her mid 20s who could be doing a job that earns her enough to pay her own rent. She's a workshy scrounger.
Or wants for her mother to house her despite having what sounds like significant MH issues, an attitude problem, and being a shit to her younger siblings who would be living in the house with her. What about those children, do they not deserve a happy home where they can feel safe?
That's the issue, not what she chooses to do to earn money. It's the fact she's not earning a living from it and expecting OP to subsidize her. Why should OP help someone who's not willing to help herself? You know, by growing the fuck up and getting a proper job so she can pay her way in life? As well as learning to behave in a civil manner towards others?
OP, therapy only works if a person engages with it. If she's using it to offload about her housemates drama it's going to teach her very little. A person has to be willing to change, otherwise change won't happen. It doesn't sound as though she's using it to sort her life out, learn to manage her difficulties or learn coping skills.
Can you not see how messed up it is to say that you get along fine with her only as long as you tip-toe round her emotions, put up with her demanding nonsense and punishments, walking on eggshells the whole time to try to avoid setting her off? When a person is nice as long as they get what they want all the time, that isn't actually nice at all because there's no consideration for others in their thinking.
Just because a therapist tells her she should move out of where she's currently living, that doesn't mean you have to facilitate it.