Winning colours - Elizabeth Moon

Heris Serrano thought her life was over when a treacherous superior officer forced her to resign from the Regular Space Service -
the only life she had ever known, or ever wanted. But captaining a rich old lady's interstellar yacht has proved more exciting - and fulfilling - than she could ever have imagined.

Having rescued some former Fleet friends and colleagues betrayed by the same officer who forced her resignation, and foiled a plot to poison the heir to the throne, Heris has at last been offered a chance for vindication and reinstatement in her beloved Fleet - and reconciliation with the family she thought had abandoned her. But it means standing alone against the military might of the Benignity, an interstellar criminal cartel more colloquially known as the Compassionate Hand. With only a few small ships and the space yacht Sweet Delight she must stop an invading fleet dead in its tracks . . .