。
She only ate lean meat.
Literal
She [topic-は] lean-meat [only-だけ] [object-を] ate.
赤身 (あかみ) means 'lean meat' — literally 'red body,' referring to the darker, leaner cuts without fat marbling. だけ limits what she ate to this one item. Unlike しか (which requires a negative verb: 赤身しか食べなかった), だけ works with an affirmative verb and is more neutral in tone — it simply states the fact without emphasizing what was excluded.