。
She looks bursting with health.
Literal
She [topic-は] health [with/from-で] about-to-burst seems.
はちきれる ('to burst, split open at the seams') is a vivid verb that combines with ~そうだ (the visual evidential 'looks like / appears about to') to give you 'looks fit to burst.' The で here marks the cause ('bursting because of / from health'), the same particle in 風邪で休む ('off due to a cold') or 喜びで震える ('shaking with joy'). The whole expression 健康ではちきれそう is a fixed admiring description for someone radiating physical wellness — the verbal equivalent of saying someone is 'glowing.'