Mindy was Rachel's best friend and taught her how to kiss.
After Rachel left Barry at the altar, Barry took Mindy to his honeymoon. When Barry and Mindy got engaged, he cheated on her with Rachel. It was later revealed that while engaged to Rachel he cheated on her with Mindy, and with Rachel's sister Amy. However Mindy still decided to marry Barry because she wanted to become "Mrs Doctor Barry Farber".
Mindy married Barry in the season 2 finale with Rachel being Mindy's maid of honor.
They divorced about 4 years later after Mindy caught Barry cheating on her with another woman, as Rachel gleefully reveals in "The One That Could Have Been".