It's possible you're misremembering or mixing up characters. Perhaps you're thinking of:
* "Brenda", played by Angie Harmon, who was Alan Harper's girlfriend in the early seasons.
* "Judy", played by Missy Pyle, who was a recurring character as a friend and sometimes romantic interest of Alan Harper.
* "Chelsea", played by Jamie Pressly, who was Alan Harper's girlfriend and then wife in later seasons.
Please let me know if you can remember any more details about the character you're thinking of, and I can help you pinpoint who it might be!