There is a great character description and analysis for each character in the novel on eNotes, so I will post Katharine's here for your convenience.
"Winston’s wife. She was a tall, fair-haired girl, and, according to Winston, remarkably vulgar and stupid. Technically, he is still married to her, though they’ve lost track of each other. They parted ways about ten or eleven years before, after only fifteen months of marriage, when they realized that she could not get pregnant by him. The Party has declared that the only reason for marriage is procreation, and in fact it is illegal to have sex simply for pleasure. Therefore, there was no reason for Winston and Katharine to stay together. The Party does not believe in divorce, just separation, so Winston and Katharine just sort of drifted apart.
Readers only see Katharine through Winston’s memory of her, and her main purpose in the novel is to show how the Party destroys love, sex, and loyalty between husband and wife."
Hope this helps! I'll include the link below as well.
Katharine is Winston's wife. They are still legally married because the party does not allow divorce.
Winston reflects on Katherine's lack of emotion several times through the novel, often comparing the daring Julia to his frigid wife.
She is Winston's wife. There is nothing much to her, as she has become and or symbolizes a standard and or ideal product of the Party, and that they are devoid of emotions. They are just cogs in a big system for the Party that runs Oceania and there is no individualism in each part,
She is Wilson's wife but isn't talked very much in the book. They were legally married, but since the party disallows divorce, even though he had sex with Julia, they technically were married to each other, and the fact would still remained as the truth.
Katharine is Winston's wife. They are technically married, but haven't seen each other for a while. Winston describes her as vulgar and stupid.