My friend is a plus size girl and we will be attending a wedding together what should she wear?

She is a larger girl, very insecure. She's beautiful though! She is a 38DD, 42 in waist. She never wears dresses, but she really wants to for this wedding. It's going to be a summer wedding but she doesn't really want a sleeveless dress. Anyone have good websites or ideas to keep a plus size girl comfortable during an outdoor, Texas wedding? She has already called me very distraught from 5 different dressing rooms, so this is the only thing I really have left to help her out. Please someone!! HELP!!!