You probably accidentally clicked on the 'Subscribe' button when viewing that thread. Go to it now and take a look. If there's a button marked 'Unsubscribe' then that's obviously what you did. (Click the button to reverse your action)
I agree Patsy must have clicked 'Subscribe' by mistake, but it sounds like she's unaware that users can subscribe to anyone's posts they're interested in and get notifications when a new response is been added.