。
She was ashamed of her carelessness.
Literal
She [topic-は] her own carelessness [object-を] was-ashamed-of.
恥じる ('to feel ashamed of, to be ashamed of') is a literary/written verb for shame; the everyday spoken alternative is 恥ずかしいと思う. Takes its object with を — the thing/action one is ashamed of. 不注意 ('carelessness, inattention') is built from the productive negation prefix 不- attached to 注意 ('attention, care'), a very common Sino-Japanese pattern (不可能 'impossible,' 不安 'anxiety,' 不要 'unnecessary,' etc.).