GR translation: broad mouton hipline

[Mike Jing]

P174.4-7  Gwenhidwy is drinking from the bottle, carrying on a running
slap-and-tickle with Estelle and getting in a fast game of
where’d-he-go-there-he-is with Arch her youngest around the broad
mouton hipline of his mother who keeps trying to smack him but he’s
too fast.

Does this mean she is wearing something made of sheepskin, or is it
something else?