It's chest fluff. Jen has had it from the start as an Audino. Outside Victini scratching Jen's face, clawing her right arm, and biting said arm, Jen has not suffered any other physical injuries unless it was of the off-screen type (like back during the Destiny Tower expedition -- Jen has had to have been banged up a bit back then though she was probably healed via eating Orans/Sitrus's or by Gardevoir's Heal Pulse).
EDIT - Whoops. I forgot once Jen stepped on a thorn when Gengar was taking her to Great Canyon back in Book 1. <.<