。
She tore his letter to shreds.
Literal
She [topic-は] his [genitive-の] letter [object-を] to-shreds tore-apart.
びりびり is a 擬音語/擬態語 capturing the sound and feeling of paper tearing — short, sharp, repeated rip-rip-rip. Combined with に, it becomes a resultative ('to (the state of) shreds'). 引き裂く ('to tear apart') is a 複合動詞 (引く 'pull' + 裂く 'split, rend') — emphasizes the violent, forceful nature of the tearing. The whole sentence is small but vivid: the mimetic + compound verb pair makes the moment cinematic.