I don't think Katherine Hepburn deserved her Oscar for this one
Katherine Hepburn was marvelous in this role as every other in her career and she certainly deserved to be nominated for this film but I am honestly puzzled that the Academy gave her the Oscar given that there were better performances both that year (by other actresses) and by Katherine in other films.
It's not that she did not do justice to her role. She most certainly did. But her character was not as complex and layered as her characters in many other of her other films and did not require much of her other than seeming concerned and righteous (which quite honestly was not a challenge for her).
While it is hard to pick her best performance, one can argue that she gave her greatest performance in "The Lion In Winter" (for which she won the Oscar the following year, tied with Barbra Streisand). Hers was a chilling portrayal of a woman who is wronged (imprisoned against her will by her own husband) but is also a cunning, manipulative woman. It is so difficult to play a character that you hate and yet feel sorry for, and Katherine did an unbelievable job in the role. While that character was complex and required enormous skill to pull off, this performance could only be as deep as her character which was quite honestly not as fleshed out as the husband's character.
1967 had many fantastic performances (though none of them dumbfoundingly good IMO). Edith Evans had a showy role (which won the Golden Globe) was favored to win the Oscar, so Kate's win was quite a shock. I cannot decide who among the five nominees I would have chosen (all were good), but I don't think it would be Kate.