I don't know if it's just me, but I can recall many occasions when Keiko was nice. She was extremely supportive to Miles after his twenty-year "imprisonment", and when he was taken to Cardassia to be put on trial. And even if she may have felt a little jealous that Miles spent so much time with Julian, she never tried to get in the way of their friendship. She even arranged for them to hang out together, when it was obvious that they were both down in the dumps. Never once did I get the impression that she "hated" Miles.
Plus she was a wonderful mother. I can't say I agree with all the Keiko-hate going on here.