。
She looked as if she had been ill.
Literal
[topic-は] just-as sick was-[as-if-かのように] appeared.
見えた is the past of 見える ('appear, look [a certain way]') — distinct from 見られた (passive 'be seen') and 見た (past of 見る 'see'). 見える here links to a まるで~かのように clause, giving 'looked as if [she had been sick].' 病気であった (formal/literary past of 病気だ) — a notably bookish register choice; spoken Japanese would be 病気だった. The whole sentence implies someone looking back on a recent moment when the woman appeared unwell — recovered now, but the look lingered.