。
It seems she was beautiful when she was young.
Literal
She [topic-は] young days beauty was [it seems-ようだ].
~ようだ (it seems/appears) expresses the speaker's inference — less certain than に違いない (must be), more measured and careful. The speaker has some reason to think she was beautiful but isn't fully committed to the claim. This evidential distinction between ようだ (seems), に違いない (must be), and かもしれない (might be) is a key feature of Japanese — each marks a different degree of certainty about the same kind of inference.