I do really wonder sometimes!
The OP asks what the 'rules' are?
Stuff the rules, to me, common sense and respect do not need rules.
A WG sends you private pictures, lets you take some photos for your own memories, they are 'PRIVATE' really it's as simple as that.
From their website, from an AW profile or another hooker site, that's in the public domain and although there are copywrite rules.
From what I would call public sites or those not connected with her business, personal Facebook page etc, that's their private life and that's where they should stay.
If you think differently that's fine but take a moment and consider how you would feel if a SP found your Facebook page and posted your pictures on UKE or SAAFE or even used them on her profile for some strange reason.