"Shari Stapleton doesn't know what to expect when she leaves her home and her boyfriend to stay at cousin Meg's for their grandmother's wedding. What could happen? Anything and everything. The biggest problem is the groom's gorgeous nephew, Evan, who seems to like both Shari and Meg. But Meg and Shari are cousins, and each has a boyfriend. Could they be rivals? Is Evan worth fighting over?" This is from the back cover of the book.
Used availability for Marjorie Weinman Sharmat's How to Have a Gorgeous Wedding
May 1985 : USA Mass Market Paperback