。
She burned her left hand.
Literal
She [topic-は] left-hand [object-を] got-burned.
やけど (kana for 火傷) is the noun for a burn injury, made into a verb with する: やけどする ('to suffer a burn, to get burned'). The structure 左手をやけどする is interesting — the body part she burned is marked with を, even though やけどする is intransitive in form. Japanese routinely treats body-part injuries this way: 足をけがする (injure one's foot), 頭をぶつける (bump one's head). The body part is the affected location, marked as if it were the object of the verb's effect.