so here are my theories on her (their) role in the second movie:
(pictures from winx-fairies)
1. there mother-daughter group trying to stop bloom and sky from getting married
2. again mother and sister of diaspro trying to get sky to marry diaspro
3. there sisters hired by sky's dad trying to break bloom and sky up
4. there the same person who is in or at the wedding AGAIN trying to break bloom and sky up
bottom line: i think this (these) large girl (or girls) is (are) trying to break bloom and sky up!
stay tuned for more!!