It wasn't about her going to the dentist as a cover to see the OM...
The true insight here is this:
She did NOT go to TKD...
Which may be evidence that she doesn't care so much about going to TKD when the OM isn't there. You were believing she didn't go because of your NC rule.. You got fooled. She probably didn't go because the OM wasn't going to be there. She could then use that as her excuse that she was doing what YOU wanted.
Her NOT going points more to evidence that she isn't so motivated about TKD unless the OM is there.. She then used her not going as a tool to get Pens to think that she is serious about reconciling...
Too early to tell. The WS doesn't usually get over the OM this fast. Be wise.