、。
After reading the letter, she tore it into small pieces.
Literal
She [topic-は] letter [object-を] read [after-あとで], it [object-を] finely tore.
~たあとで (after doing) establishes the sequence: reading came first, tearing came after. 細かく (finely, into small pieces) is the adverbial form of 細かい (fine/detailed), describing how she tore it — not just in half, but into small fragments. 破る (やぶる) means to tear or rip. The deliberate destruction of the letter after reading it suggests strong emotion — anger, grief, or wanting to erase what was written.