Not only it is weird, it's inappropriate. A commitment to the therapy work is the obligation one makes to oneself only, not to the therapist. You have no obligations to your therapist and she has no right to demand a doctor's note. If she feels that she cannot be effective if you miss sessions, that's a different issue, but the cancellation policy should be clearly outlined in her informed consent. If the doctor's note wasn't mentioned as a requirement prior to your initial appointment and if you didn't agree to comply with this before seeing her, she has no right to impose this rule right now. In any case, this is a very stupid rule for a therapist to have and certainly not consistent with the purpose of therapy. When the client says she was sick, this should be accepted without a prove. If skipping session becomes a regular pattern, then the therapist may address it by asking if this is a good time for the client to be in therapy at all. But to treat therapy as if it was a full time job where you have to show up regularly is dumb and counterproductive.