It's her choice and you might not like the answer.....good hygiene is very important

From reputable reviewers, If you spot a trend of CBJ vs BBBJ then she may just do it with some not with all, I guess majority of reviews showing BBBJ if not all, will tell you that is what you should expect.. Please do not ask explicit question regarding services, it is a red flag and most providers will not let you book with them, that is why reviews are in place, to spot trends and in most cases, know exactly what to expect on a session.

Perhaps the reason is that she developed a canker sore in her mouth and she is thinking of your well being on account of that.

More than likely I would have suggested she bring this up prior to the appointment.

I'd go with it, rather than risk killing the mood.  Depending on the atmosphere I would ask afterwards.  I usually go a few rounds, if that's the case for you you might ask in between.  Depending on circumstances I might make explicit mention in my review that it was a cbj with a ymmv caveat.  

Sometimes the reason given is a simple one, and it isn't always a bad one, dental work that morning, for example, would put her at increased risk, so if you were to see her again you would might receive different service.

squeaky clean when seeing a provider.  If necessary, take a quick shower when you arrive and be sure to wash the privates.