I Felt Like I Was Watching a Mash Up of Three Movies (SPOILERS)
"Just Friends" (formerly unpopular and unattractive teen grows up to be good looking and successful, revisits childhood home)
"27 Dresses" (main character determined to show groom how phony and evil the perfect bride-to-be really is by sneakily showing incriminating video footage at the rehearsal dinner, resulting in cancellation of wedding by groom; later there is reconciliation )
"Bridesmaids" (famous musical act that has relevance to the bride appears at the reception to sing signature song)
Yes, I know "Bridesmaids" was released after this but it still had the similar element