So i'm about to see a provider for the first time this weekend.  We have been emailing back and forth for a few weeks now, and I was wondering if its acceptable to ask the provider about specific acts before the session.

as the previous response indicated, the answer is NO. Most if not all provider's websites state the rules. and usually mention any explicit questions about sex will have the escort stop all communication with a hobbyist.   Where did you find her. You need to learn how to research the provider you want to see. The juicy details of the provider's TER reviews will let you know what she offers.  

Like said above, it's never OK to ask about specific sex acts via any type of communication with her.  If you don't know what's on her menu by now, you have not done the proper research on her.

Swim

There is a TON of information there that is invaluable.

you should check her TER profile.  Just because she HAS reviews does not mean they are good!  I've seen ads with links to her "TER REVIEWS"...  but when you read them, they say stay away.  Clearly figuring guys are too lazy to check.  Don't be lazy.  
 
The profile form will fill in a lot of blanks but you really need to read the latest reviews including the details.  Yes, you'll need VIP.  VIP is cheaper than a spoiled date.  
Any discussion of sex acts will seem like a LE sting & she'll likely cut off all contact.

And I would say something along the lines of, "I have read your reviews and was wondering if the reviews are indicative of the type of session I would be getting."  Read her response.  If she is engaging, then ask her if it is okay to ask about something specific.  She may just say that the reviews are indicative and that everything else can be discussed in session.

If you are worried about upcharges, simply ask, "Is the rate on your site all-inclusive, or is there tipping involved?"

That oughta make it pretty clear, and you should be able to avoid offending her if you take this approach.