Remember Yuna originally planned to do everything by herself so she had plans to try and send him during the wedding. She wanted to be independent, strong woman type thing.

But then Tidus and the rest of the goons show up and her whole plan so I think that she's a little panicked and doesn't know what to do now. Her whole six weeks of thinking what to do with Seymour have just gone down the toilet seat. So it makes sense that she was a little stressed, worried and didn't know what she was doing in a way. She needed to think of a new plan and everything wasn't going the way that she originally hoped that it would.