I would probably skip the event but tell the therapist I was so nervous about meeting her and about this transition in my life that I was tempted to see her ride, just to quell the first-meeting nerves. That will help her appreciate how anxious you're feeling so she can help you.

However, regarding your question, no, it is not stalking to see someone in a public event, even one that's not widely advertised. Watching her ride won't do her any harm. Would be different to google her home address and go stare in the window, which might scare her. Still... I don't think it's best.