。
She seemed to be slacking off.
Literal
She [topic-は] is-being-lazy [seemed-ようだった].
怠ける means 'to slack off, neglect one's duties,' used in resultative ~ている form here ('was being lazy'). ようだ is the inferential 'seems / appears,' built on observation or reasoning rather than hearsay. Past form ようだった ('seemed' — past) describes how the situation appeared at some past moment. Distinct from ~らしい (apparently — based on report) and ~そうだ (appears — based on visual cues).