No, she's certainly not a slave. This is an act of her own free will, and as far as she's concerned, a favor to the entire neighborhood. There's still a of work to be done untangling his hair, but it might as well be accomplished in warm water. Maybe it will even relax him a bit.

"There are hot springs further in the forest. They're at a good temperature for bathing, or so I am told. I haven't used them myself, but I know others who have. Would you like to go there?"

Zelda can't really bring herself to do the whole outdoor bathing thing. She feels exposed in clothes most people consider modest, taking everything off outside would be far too uncomfortable.