Means she put on (wore) her robe to go to the bathroom. Now she has returned to the bedroom taken off her robe (and hung it up on a hook) to return to bed.

Perhaps she put on her bathrobe[ dressing gown] to go to the toilet because it was cold in there and then when she came back, she removed her bathrobe because it was warmer in the bedroom.

She has taken off her robe and now she hangs it up on a hook somewhere. Nice.

A robe is either short for 'bathrobe' which is a loose fitting garment that looks like a coat but is often made from absorbent fabric (toweling or just cotton) and is worn before or after bathing or it refers to a dressing gown which is a garment worn over night clothes when not in bed . In your sentence, and as Brian said, Judy probably put on her 'robe' to go to the bathroom and put it back up on a hook before returning to bed.