Katherine "Kathy" O'Connor Zbornak was the third ex-wife of Stanley "Stan" Zbornak.
While she inititally conveyed to Dorothy, without realising she was Stan's first wife, how much she loved Stan, it seems the marriage ultimately failed. It is mentioned that she threw Stanley out on Christmas Day 1989, but later took him back. However, she was never mentioned again afterwards, and considering Stan almost remarried Dorothy, they must have divorced sometime prior. (The most likely explanation is that the writers forgot of her existence or lost interest in developing her character further.)