Is the stepmother considered a blood relative, and is it obligatory to maintain ties with her?

The father's wife is not considered among the kinfolk whose ties must be maintained, unless there is another kinship relationship. She has the right to dutifulness and kindness as an act of showing dutifulness to the father, due to the Prophet's (peace and blessings be upon him) saying: "Indeed, the most dutiful of deeds is for a man to maintain ties with the loved ones of his father."