Not fully booked according to her diary - more like fully empty.
Yeah that's an interesting point. In my experience quite a few girls seem to be like that, even those who I'd strongly believe when they say they're really busy or booked up. It's also sometimes the case that their diary is totally open even when the WG says to look at her diary to see her very limited working times or whatever.
A lack of bookings through AW could also explain why her feedback is so relatively low (considering how long she's been on AW and how keen some fluffies on AW are to throw positive feedback at WGs).
Sometimes WGs do falsely claim to be fully booked when they're not actually here/available, in order to create the illusion of demand (and therefore encourage punters to book and to book soon). However, I imagine that's still fairly rare. And of course if she is actually here, it would be very silly to lie on her profile about being fully booked. It's also perhaps a bit excessive/a waste of money to pay to put your phone number up if you were never actually planning to work that day. Sometimes though they just forget to update their profile.