Rebecca (left) with Diane.
Rebecca Prout (played by Julia Duffy) is a guest role character during the Season 1 episode Any Friend of Diane's. Slightly before her appearance at Cheers, she was dumped by her unseen partner Elliott. It is never mentioned whether they were married or not, although Diane mentions they were "together forever".
Rebecca goes to Cheers in search for a man who is "peasant-stock, tall, dark, strong, hairy arms, but most important, he should be unintellectual, one-word sentences." Early on in this search, she finds Sam. However, Sam is not interested in Rebecca's intellect and desperately tries to avoid her, even to the point of escaping out the window on their first date.
An interesting fact is that Julia Duffy, the actress who played Prout, was one of the original choices to play Diane.