That would mean that that she is living with the family of some other woman.
"sia" refers to the subject "lia"/"ŝia"/"ilia" refers to some other person(s) in the context but not to the subject.
"Petro vizitas Brunon kun sia koramikino." (Peter is visiting Bruno with his (Peter's) girlfriend) "Petro vizitas Brunon kun lia koramikino." (Peter is visiting Bruno with his (Bruno's) girlfriend)
There isn't one. Sia is simply a reflexive pronoun. It works with all genders.