。
She's worried about your health.
Literal
She [topic-は] your health [object-を] is-worrying.
心配する treats worry as something done to an object — XはYを心配する is 'X worries about Y,' with Y marked by を. English 'worry' takes 'about,' but Japanese fits the worry-target into the standard direct-object slot. The ongoing state ~ている is appropriate for an emotional state held over time. 君 again sets a slightly intimate or casual masculine-leaning tone for the addressee.