。
She broke her left leg because she fell.
Literal
She [topic-は] fell [because-ために] left-leg [object-を] broke.
~ために here is causal ('because'), not purposive ('in order to') — context makes the meaning clear, since nobody falls on purpose to break their leg. The causal ~ために is more formal than ~から or ~ので and is common in written accounts and reports. 左脚 uses 脚 (leg, the whole limb) rather than 足 (foot/lower leg).