I think rather than Sanae hating Kyoko's dad and thus transferring those feelings towards Kyoko, i got the feeling that Kyoko was an unintended pregnancy. I can't imagine Sanae loving any man enough to hate him. Sanae probably never wanted kids in the first place, kinda like Moko, and when she found herself pregnant decided to keep the baby for some odd reason. Maybe she felt that a child could give her the emotion she lacked, IE: love. When she realized that a child was more needy and time consuming than she could handle, she abandoned her to friends she felt could love her as she could not. Maybe there was an incident where she prioritized her work over her sick daughter and felt guilty about it afterwards.
Basically, i really feel that Sanae's lack of love is a personal problem rather than the result of some traumatic event. (being dumped, etc.)
I've always had a feeling that Kyoko's mother loathes her daughter because she recalls her of Kyoko's father, a man who she deeply hates. That's so wrong on so many levels, but I just wanted to know what you think of that idea...?