Worried for my daughter
You say your daughter had a previous relationship with a controlling addict, so good on her for having the strength to end it. I see that as a very positive move on her part. She seems like a smart woman. You didn't say whether she is or was also addicted to substances, so I'm hoping that means she's not. Is she? Because if the prostitution is what she does to feed an addiction, the root of the problem is the addiction, and that's what she needs help with, not her job.
If she's not on drugs, she is healthy and supporting herself, that's great. As for how she's supporting herself you may not like it, but if she says she feels empowered by what she is doing, maybe she does..? You said she feels it's the 'best thing she's ever done', and those are strong words. Do you think this is a lie, or does she mean it? Does she seem truly happy? Is she taking care of herself in a way that means she's unlikely to fall into another controlling relationship? Does she know her own worth and mind? Is she being safe? If the answers are all yes, these are the positives you could focus on. Because when it comes down to it, if she wants to do this work you can't really stop her (I'm presuming she's an adult).
I know it clearly makes you upset and uncomfortable, so this might not be what you wanted to hear. But if you want to maintain a relationship with your daughter you may need to find ways to accept the things about her you don't like. There's a chance if you push her to feel ashamed of what she's choosing to do she might end up pushing you away altogether.
Just another perspective to think about