Remember the ladies are first and foremost ladies, each has differing wants and desires.  If you straight up ask her she may tell you, she may hint so be perceptive.  You should lead and let her know what your limits are, dinner, travel, party, ect, flowers and BFE should always in the plan.   Be careful with surprises, I've had one really bite me in the butt.

Or are you paying her normal rate?  Did you book for a multi-hour date?  If your evening includes OTC time, I agree with the other poster and just ask her. Don't forget, you are not her real life BF. If she is good at what she does, you may feel like her BF, but you are not.

Much depends on if you have an extra special connection with her and she wants a BFE.  

I realize you asked the ladies this question, just thought I'd add my $.02.

BTW- have you been holding back and just now ready to give her an awesome performance?  (tongue in cheek)

I would suggest taking her to Lord Fletcher's for the best dining ever (952) 471-8513!
They have the best steaks in the State!

Remember, even though it is her birthday, you are still a client, not an SO.  A tip or something you know she likes is nice.  Just don't give her cause to worry that you are trying to cross boundaries.

...a spanking on her birthday.  I was happy to oblige, and we had a great session of spanking and then cuddling.  

Don't overthink this ....

I can only speak for myself but simply spending time with a respectful gent would be a great gift.
That said,  I would not refuse a cozy home-cooked dinner with candlelight & soft, romantic music & a little red box.   Cash tips are a nice thought also.    Flowers are great too!  Yellow roses are my favorite!!!!

And, as someone said, a shopping trip to MOA would be SWEET!!!   Or, a weekend away with a trip to the mall and a sex shop!   Oh my!!!!

Just have a good time!

If she is spending time with you on her birthday of all days, most likely she enjoys seeing you. You don't have to bring an expensive gift, just bring yourself and create new memories. xoxo