its never "necessary" to tip---that's why its a tip and not part of the set fee. Like any other service, if you are especially happy and want to show it, tip.  But as many people have commented on in the past, the best "tip" is a re-book.

I don't generally tip, but usually bring a small gift(s) instead. I find it to be more personal.   There is always a lot of varied opinions on tipping and gift-giving, so you just have to do what you are comfortable with. But you should never expect better service just because you tip or give a gift.

runningman

Give a nice gift if you wish, let them know you had a good time, reschedule if you can (perhaps tentatively in your case), but most importantly  give them the EXACT tip amount spelled out in my subject line.  That's what they all say they were EXPECTING, therefore it is absolutely necessary that you give them that exact amount in the tip!

...is to book with her again.  Second best is telling your like-minded friends how wonderful she is so we can fill her date book and pocketbook.