。
She bandaged the wound.
Literal
She [topic-は] wound [on-に] bandage [object-を] did.
包帯をする (to apply a bandage) uses the common pattern of [noun + をする] for performing an action associated with that noun. The に marks the location where the bandage is applied. 傷口 (wound opening) is more specific than 傷 (injury/wound), referring to the actual site where the skin is broken or cut.