Kumiko's motivations are hard to understand. In her words, she is, "A weak mother." She pushes her daughter away, partly out of anger and partly because she does not feel that she is prepared to be her mother. She used to be a happy-go-lucky woman who was overenthusiastic about life. But when raising Haruka proved difficult due to her supernatural ability to read minds and her husband gradually ceased to come home, she buckled under the pressure. She became openly bitter, and due to her drinking in the final episode we learn that she is an alcoholic.

(http://kotoura-san.wikia.com/wiki/Kumiko_Kotoura)