I'm having a hard time believing that TSwift would crash anybody's wedding, but the bride's mother tells the Boston Herald that's exactly what happened. 

Apparently, she was invited as a guest of Conor Kennedy's.  He never RSVP'd until an hour before the wedding last weekend.  That's when he texted to ask if it was OK if they showed up. The bride's mother, Vicki Gifford Kennedy, tells the Herald that she texted "Please Do Not Come", reportedly because she had fears that Taylor would upstage the bride. Well, Conor and Taylor showed up anyway. And when they did, Vicki Kennedy wasn't shy about asking the star to leave. Kennedy said it was like she was "talking to a ghost, she (looked) right past me."

Taylor's spokesperson says the story is simply not true - that the bride repeatedly thanked her for being there.

Here's what I believe could have happened.  I believe that Conor acted like an 18 year old kid and DIDN'T RSVP.  I believe he must have had every intention of going...invited Taylor to be his guest - then, when he went to grab the invitation to punch the address into his GPS to head up to Boston to the wedding, found the unsent RSVP along with the invitation.  He slapped his forehead, texted, and got the "Please Don't Come" reply, which he chose to ignore because his new girlfriend was all dressed up...and he was not eager to display his faux pas to her.

The blank stare from Taylor Swift can be explained by pure shock.  She must have been mortified to have the mother of the bride ask her to leave a wedding.  That could be why the couple left the reception during dinner (presumably so she could let Conor have it for embarrassing her), then returned after the meal for dancing.

I believe the bride really, truly was happy to have Taylor there, that this was just a case of the mother of the bride over-reacting to a bone head move from an 18 year old.