I do online therapy so most of my sessions are recorded and I've found those records invaluable. In my state, two-party consent is required to record a conversation, meaning I'd be breaking the law to record her without permission. Whether your state has a two-party consent law or not, it's important that you have an open, trusting relationship with your therapist, and that requires that you have her trust too. I hope you'll discuss it with her and that it's a positive conversation.