Well, she might not be his romantic interest. She was the one who wanted to catch the bouquet, you can see in that scene her arm reaching out to grab it, but Pippin catches it first. So, she stands there trying to act as if nothing happened, and Pippin looks at her as if to say: 'Ha! I caught it, not you! So now I'll go marry Diamond.
' Btw, there is no Diamond listed in the credits, which means she can't be Diamond.