I would ask permission. I personally wouldn't be able to record someone else without their permission as it would feel to me like an invasion of their privacy.

If she says no or that she's not comfortable with it, you could always bring up that you would like to record it so that if you forget what you talk about with the potential new therapist (this is a meeting with one of the two she's found for you, right?) you'll be able to refer back to the session. But you would need their permission too.