I would define what you mean by "supervision" and why that matters to you? Are you thinking they can catch your therapist before a mistake is made or you can think of something going wrong in a wider context, imagine it could be the supervisor's fault instead of your therapist's (the supervisor made me do it :-) or what? It sounds like you are trying for some sort of safety net? If your therapist turns out not to be "good enough" for you, her having a supervisor isn't really going to make a difference?

Are you going to have supervision being a client?