I frequently will mention in my initial e-mail that I am a TER member, only as one more avenue that she can use to check me out.
I never, never, mention the possibility of a review until after the meeting has ended.  If it was a good experience I will take her wishes into account as to whether she wants reviews or not.  If the experience was a bad one I don't even bring it up, because I will write that review in any case.
IMHO, to tell her at the beginning of a session that it will be reviewed in the hopes of getting "more" seems... I dunno... sleezy...

other than perhaps in your initial contact with her you are a member here... you may or may not decide to do a review... but her performance should be based on just the session with you, nothing else.

Some referral services (e.g. Preferred411) have as part of their profile whether you review and on what boards.  If you and the ASP use those services the ASP can get that information up front.  If not, as PocketFisherman points out by way of introduction you might mention your handle on various boards and if the ASP wants to do the research the ASP can ascertain if you post reviews and the nature of your reviews.  And I also agree with PocketFisherman, if the session was a good one I'll ask the ASP how they feel about reviews.  I usually ask that at the same time I ask if it is okay to use them as a referral.  If you've done your homework you should have a feel for whether the ASP allows reviews.