NRMH - I've just read back through the entire post and you have asked several times, probably rhetorically, "what can I do anyway?"
It seems to me that you want to believe that she's happy, that it's an informed choice, that she will be absolutely fine and unscathed.
Because if all of that is true, you could absolve yourself of any responsibility you might feel towards her and not worry about actually having to do anything to help her.
You say that you want to understand why some people find it necessary to judge you for what she is doing. I don't think from your posts that it is that people are judging you for what she is doing; they are judging you for not trying to do anything about it (that's not to say that you can or should do anything about it but that seems to be what you are being judged for).
If you need to understand why some people are judging you for not doing anything, that suggests a lack of knowledge (and I don't mean to be patronising here) about prostitution. Or perhaps they are showing a lack of awareness? Could I suggest that you do some research and then you could understand either why people might be judging you or you could arm yourself with facts/figures to give to them to justify your own stance and her choices (of doing nothing) because you will then think that prostitution is fine as a job.
You still seem unsure as to what you think of her choice.
In answer to your questions, should you stop her - I would say, yes, of course you try as I hope I would if I was in your shoes. Your second question - would that be possible anyway? Very possibly not but I'm not sure I could stand back and let a young relative be a prostitute.
If something happens to her at some point, would you be easing your conscience by telling yourself that it was her choice?
The guys I know who all use prostitutes/strip clubs put forward the "it's her choice" argument every time. It absolves them of any responsibility (i.e. making a choice themselves of not using the prostitute/lap dancer) and it seems that that's what you're doing here.