If you are only reducing the score due to leaving certain services out then I don't really get how there's a problem. It sounds like you want to give her the maximum you can given the limits on what score can be given. If so then she's getting the top rating you can give. Right? That should be considered a very good review and anyone reading it, who understands the scoring system will see it that way.  

Or am I missing something

If she asked to leave out the extras, I would leave out the extras. If you feel that like she deserves a 10 in performance, give her a 10. If TER doesn't like it, let them change the score.

this is what I would do - and have done.....

I would first of all respect her wishes with respect to what is revealed in the review -

this does limit her score, but you can mention in the juicy details section that her score is limited by TER scoring rules but that if it were up to you, you would have given her a score of _________  based on the quality of your interaction...

Say something like, "She's still figuring out just where her limits are, and YMMV, but I had a great time."  If TER drops the score, that's on them, not you.  She'll want to figure out how she's going to communicate limits in the future, as clients will be checking them out.  This is one place where "Don't Know" might be the right answer -- just because a certain thing happened for you, does not mean that it will (or *will not*) happen for someone else.

If you get a PM asking, "Hey does Lady X do Activity Y?", you might want to say "Sometimes -- it's not completely out of the question, but I got the impression it wasn't always on the table."  That's different than a review, IMO.

Score in accordance with what is required for rating under performance. Speak highly of her in the description but as far as points go leave out the extras she won't perform for everyone and score accordingly.