I don't know her, but if she's like other therapists, I think she's likely to take the tack that it's up to you. If you want to go, go. If you don't, don't. Don't decide based on whether she's okay with it or tells you to come in. You're the one with deciding power here, and to turn it over to her not only isn't a good idea, you're doing yourself a disservice.

Eta: what i'm trying to say is, don't be passive here. You made a decision...stay with it. It's actually a step towards feeling more in control, not just of therapy, but of life in general, including all the anxiety you feel about exams.