Winning Colors — Elizabeth Moon

"The difficult we do immediately. The impossible may take a little longer:..."

Booted from the fleet as her reward for saving a villainous superior from catastrophe, Heris Serrano has been marking time captaining a rich lady's interstellar yacht. But though she was hired only to chauffeur Lady Cecelia from pleasure to pleasure aboard the good ship Sweet Delight, things happen when Serrano is around.

After saving a Prince Royal in Hunting Party, and deposing the prince's father in Sporting Chance (with the enthusiastic assistance of her 90-yearold employer, who has never had so much fun in her life), Heris has at last been offered a chance for vindication and reinstatement in her beloved space navy. All she has to do is save the galaxy from an interstellar mafia gone berserk.

The first step will be to take one destroyer, two PT. boats, one ore scow, and--oh yes--the space yacht, Sweet Delight, and stop an invading fleet dead in its tracks. Impossible?
Well, it may take some time....