Once a Hero — Elizabeth Moon

TRUE GRIT

Esmay Suiza wasn't a member of a great Navy family like the Serranos. She'd had to make her way on grit alone, which meant it wasn't likely she'd ever make admiral and "hoist her own flag." Well, that was fine with her: all Esmay wanted was a secure berth where she could be part of something greater than herself and otherwise just live her life in peace.

But what we want or think we want from life and what we get are seldom the same -- and one day Esmay found herself in the middle of a space baffle, and the senior surviving officer in a mutiny against a traitorous captain. Suddenly she has no choice: she must take command and win--and thereby become both the youngest and lowest ranking member of Fleet ever to win a major battle.

While Esmay may not want to be a hero, it looks like she just can't help it, because Once A Hero....