Katherine "Kathy" O'Connor-Zbornak was the third ex-wife of Stanley "Stan" Zbornak.
By chance, she meets Dorothy - Stan's first ex-wife - at the bar in the hotel she is due to marry Stan in. However, she doesn't find out right away that she's talking to Dorothy herself, and confesses she has cold feet about getting married, having never been married before except to her career. Katherine was afraid Dorothy might want Stan back, and while Dorothy herself did feel that way, after speaking to Katherine, decided to put aside her feelings and give the couple her blessing.
Katherine is only mentioned a handful of times afterwards - Dorothy asks Stan if the 'current Mrs Lucky' has any idea what a maggot he is in Season 5. And later in that season, she threw him out shortly before Christmas Day. However, she later took him back. That was the last time she was ever referenced, however, as in Season 6, Stan and Dorothy begin courting again and even almost remarry. For whatever reason, Katherine and Stan must have divorced.