It will be well established if she allows more than one pop in her reviews. You might be referring to her profile but don't go by that as much b/c the first guy that sees her sets the profile and may put in "sometimes" by mistake or only could pop once so he didn't know and just chose "sometimes" as a guess.
Guys almost always discuss how many pops they had in the "juicy details" section (only available to VIP members. If you are not one, it is well worth the price.) of the review. That is where you will get your best info.
If you are VIP, you will also have access to TER's pm system, which you can ask her reviewers directly but privately, if she does more than one pop, or any other sex act you want to inquire about.
No, I would def NOT advise you to ask her over the phone or by email. In many cases you will get hung up on or not have your email returned and put on her DNS list. Best time to bring it up would be after round one, unless she asks you at the very beginning "what do you like?", then at that point she opened the door and you can ask. But like I said, if its important to you, you should have that info b4 you even walk into the room.
A girl always has the option to decide what she will do or won't do with you sexually, regardless of what she has done with others. But she also knows you could gig her with a bad review if she is widely known for being a multi-pop girl and gives you just one. There are no guarantees, but if you do your homework thoroughly, you will be satisfied with her menu in the vast majority of cases and should not have to pay extra for more than one pop