。
She tore the letter to pieces.
Literal
She [topic-は] letter [object-を] in-pieces ripped-apart.
ばらばらに (into pieces/scattered) is a 擬態語 (state mimetic) describing the result — the letter ended up in disconnected fragments. Combined with 引き裂く (to rip apart), it creates a more complete picture than 引き裂いた alone: she didn't just tear it, she shredded it. The mimetic ばらばら conveys separation and disorder — things that were whole now scattered apart.