In the Song of Deborah, who looks through a window asking why Sisera's chariot is delayed?

Answer: Sisera's mother

Sisera's mother peered through the lattice, lamenting his delay, while telling herself he must be dividing the spoil.

“Sisera’s mother looked through the window; she peered through the lattice and lamented: ‘Why is his chariot so long in coming? What has delayed the clatter of his chariots?’”— Judges 5:28 (BSB)