What is the ruling of the Sharia regarding a man's treatment of his stepdaughter (his deceased wife's sister, whom he raised since childhood) as a father treats his daughter, in terms of kissing her head, touching her, and seeing her hair, after she has grown up and married, and what is the Sharia guidance for him in this situation?

The wife's sister is a stranger (non-mahram (definition)) to the husband, and she is not among his unmarriageable kin (mahram) unless a prohibitive degree of kinship through suckling is established. There is no consideration for the fact that he raised her or for his feeling of fatherhood towards her. Therefore, it is unlawful for her to uncover her head in front of him, or to shake his hand, or to be in seclusion with him. Both spouses must comply with Allah's command in dealing with non-mahram women.