What dress should I wear to my aunts wedding?

Hi, i am a 13 year old girl and I need help. My aunt is having her wedding in October and I only have two dresses in my closet...none being appropiate for a wedding. If you could please help me ind a good, pretty dress for this wedding it would mean so much to me. I barely get to see my aunt so i want to look my best. oh yeah.. i WILL NOT be standing up in the wedding and i want to dance so no tube dresses. i want something with straps. Thanks!