。
As soon as she read his letter, she tore it up and threw it away.
Literal
She [topic-は] he [from-からの] letter [object-を] read [as soon as-とすぐに] [tore-up-and-discarded-破りすてて] [end-up-しまった].
Three things to notice. The conditional ~と here gives a near-immediate consequence ('as soon as'), reinforced by すぐに. 破りすてる is a compound verb stacking 破る ('tear') + 捨てる ('throw away') — 'tear up and discard.' And ~てしまう closes with a sense of finality and emotional weight: she didn't just throw it away, she did so decisively.