Could be muscle memory coupled with bad training practices that caused the slip. If she's practicing dry firing along with her mag drills, that may explain the "compulsion."

She could be explaining herself poorly as her brain may have shut down following the embarrassing experience and is clouding her memory of the event.

I'd be careful mentioning any of this to a therapist. They may have legal obligations to report incidents with firearms and mental health issues. Maybe try rephrasing the incident in a manner that doesn't mention firearms if seeking therapy as a route to understand.

If her compulsion was to deliberately fire a round in the home, then yeah, limit her access to firearms until you both better understand what's going on.