Warrior Queen by Karpov Kinrade

In ancient Pompeii, slaves are bought and sold for household chores and sex. A mysterious queen moves among the elite, meantime secretly helping the slaves to escape. Eventually her life is also in jeopardy, and as the volcano erupts she and the slaves attempt to escape while being chased by the military.

It's the first century, and Rome rules the world. After her husband's death, it's left to Boudica -fierce Iceni warrior, wife of a king, and proud mother of two daughters- to unite the fractious tribes of Briton and stand against the oppressive Roman Empire.