It’s known that a man should not say hello to a woman. What if she said hello to me, what do I do? And is a man allowed to say hello to his niece and sister in-law?
In a place where the custom is to say hello to a women, it is commendable to say hello as well as reply to greetings, as this is not a greeting that contains any promiscuity, or affection, and on the contrary may result in a desecration of G-d’s name.
In a place where it’s not the custom, its prohibited to say hello, as this is a portrayal of affection, replying should be respectful and curt.
To family members (sister-in-law, niece) one may say hello, and speak work related speech only, and minimizing small talk as this leads to issues.