Is it normal for girls to wear thigh high socks in bed? I would imagine that it would cause you to sweat a lot or it would feel uncomfortable while sleeping, never mind the fact they would probably cause impressions in the skin where the sock's rim tightly digs into your thighs for a long period of time.
They also don't really seem to serve much of a purpose, if your legs are cold just get under the covers.
In stark contrast to the poor logic of wearing thigh high socks in bed, I admit that they certainly are quite appealing. I can definitely see them serving a purpose if she has a partner.