i am visiting LV soon and want to arrange a threesome with a well reviewed provider. Her web site warns against any reference to sex in our correspondence. So how does one get into the subject of virtues of potential alternatives for a threesome?
She has been reviewed with several other ladies so there are multiple alternatives. Should I go for a say in the choice or just leave it up to her?

just contact her and ask if she would like to have an extra friend for a visit.  Maybe over wine and cheese.

Be direct without being specific

Well, I guess I am slow but I am not sure if you are asking if you have a say in who the other lady is or what the three of you will be doing.

If your concern is which lady, then read the reviews of the other ladies and tell her which one you would be interested in having join. You certainly have a choice in that! You could even inquire if she would consider someone you want that she has not done a double with.

If your concern is asking about specific things you will be doing in the session, that is what she is referring to being a big NoNo.

Ask her if she would mind if you brought someone along on your date.  If she doesn't, is there anyone she has been out with and enjoyed their company before.

Simple, delicate but right to the point.

Have fun!!! They are highly recommended.