Is it permissible for a woman to have her hair straightened by a man, knowing that the questioner wears a hijab and does this to please her husband?

It is not permissible for the wife to do that to please her husband, because there is no obedience to a created being in disobedience to the Creator. She must inform her husband that whoever approves of his wife committing a reprehensible act is considered a cuckold (dayyūth), and a cuckold is deprived of Paradise.