OP - I've just read your post again and am interested by some of the language you use. I also think that this post is more about you than about her.
You say that she "appears fully happy with her choice": this would imply that you don't quite believe the image that she is presenting and that you are questioning her happy front (which I would also do if I was her relative). I wonder why this is? Do you have an innate sense of worry about her even though she seems "happy" with her choice?
You say: My question is what do I tell my friends/acquaintances if they ask about her.
If you are supportive of her choices, why does it matter what you tell your friends, whether you've had an aggressive reaction or not?
Why did you feel the need to name change for this post if you are so supportive and unconcerned about her career choices?
You say, I cannot see how I can stop her, implying that you have thought about it and want to (as I imagine a lot of people would, quite naturally). But why would this even cross your mind if you think her choice of job is ok?
However she is part of the family implying that blood being thicker than water etc, you'll support her - which I respect.
Many people are very judgemental (of me for somehow "allowing" this to happen): This is where I think the nub of your post is. You seem to be feeling judged for not stopping her and for having a relative who is working as an escort.
You feel some pressure, internally and externally, to stop her and it appears that you feel it's a negative association.
It does seem to me from both the language you use and from the fact that you've come here for advice that you are not fully happy with her choice and that you suspect that she is not happy with it (as you say she "appears happy".
I do agree that the question of intervention is a difficult one, her being an adult woman etc. However, I wonder if you have posted for reassurance that 1. there is nothing you can do, and 2. that, yes, she doesn't just "appear happy" in her choice, she actually is happy with her choice.
You seem a little torn between wanting to support her choices and feeling uncomfortable with them.
I don't know the situation fully, and I don't know how close a relation you are to her so it's difficult to know what to advise you to do. However, I can only think of what I might do if it was a similar situation and I think I would approach her closer relatives (e.g. her mum, if she's around and willing to listen) and express your concerns. If you want to absolve yourself of responsibility, that's one way of doing it.
If you are confident in her choices, then I would also suggest telling your friends that this is the case. If you genuinely believe that she is happy and that this is good job for her then presumably you will have no qualms in expressing this to your friends.