。
She fell and hurt her knee.
Literal
She [topic-は] fell [and-て] knee [object-を] hurt.
A sequential て-form chain: 転んで (fell) → ひざを痛めた (hurt her knee). 痛める ('to hurt/injure') is the transitive form — she injured the knee — as opposed to 痛む (intransitive, 'it hurts'). ひざ is written in hiragana rather than the kanji 膝, which is common since the kanji is complex and not in the standard jōyō set.