Bismihi ta'ala
According to what our esteemed jurists say, it could be makruh to initiate a salam to a non-mahram woman, unless there is a valid purpose for it. And if the salam is done with lust, or falling into fitnah, then that of course must be avoided.
As for replying of a salam, if it does not entail lust, then she must reply, if it was specifically directed at her.
And Allah knows best.