Double Wedding by Rosamond du Jardin (1959)
Graduation seems terribly far away to Pam and Penny, as they start their second year of college, especially since they and their fiancés agree that graduation should come before marriage.
But college days are crowded days and many things happen to speed the waiting. One of the most intriguing of them is Pam's growing friendship with lovely, unhappy Geneva Day, who had been so unfriendly during the twins' "showboat summer"!
Then sooner than Pam and Penny ever dreamed possible, it's commencement time--to be swiftly followed by rice and old shoes! (from the back cover)