“Never mind. Never mind. she had a great old life—”
-- Hagrid consoling Harry (DH5)
She is hit by a Killing Curse just as the battle begins.
The Battle of Seven Potters began about 9:30 pm, just as it was getting dark (the sun set at 8:56 on 27 July 1997). Hedwig was killed just minutes into the conflict, which would be around 9:40.