My companion has a wound - how do I heal?

[SeanO]

When I changed to lead a battle as a companion (Mya Stone)  she took an injury to her face and now has -1 charisma.

Back on the party map I can't seem to heal her wound.  I have tried healing my wounds (player charactic) with Sylva but this doesn't seem to affect Mya.

I thought there was an option to switch party leaders on the campaign map as well, so I could switch to Mya, talk to Sylva, and then heal the wound, but I can't seem to figure out how to do it. Can anyone help?  How can I heal Mya's wound?   

Thanks