She first appeared in "Merry Thanksgiving" when she told Charlie that she needed to tell him something important over coffee. Charlie thought that she would give him another opportunity but, Lisa told him that she was going to marry. Hence, Charlie tried to show her that he's a family man, inviting her and his whole family to celebrate Thanksgiving to conquer her. But the plan did not work and finally he said goodbye to her congratulating her on the wedding.
Lisa reappeared in the episode "Yes, Monsignor". She told to him that she was divorced and had a daughter. After he became fond of Lisa and her daughter, he got to earn her respect and returned to being significant others. But soon, Charlie began to tire of her daughter (because he kept bothering him and Lisa when they had sex) and ended their relationship.