There's also the question of possible escape, whether she wishes to, is encouraged to, and what happens when/if she attempts it.

Is her society pro-slavery or is it an underground subculture? Do attitudes change over the period involved? You mention an anti-slavery girlfriend for a major character; is she the aberration or the rule?

Is she trained to A) Accept, B) Enjoy or C) Despise her status? Does she have mandated rights (as the Romans did for slaves) or is she considered an animal (as most of the slave states of the Old South operated things)?

Remember, you're not just creating the characters, but the entire world.