Alice Greenwood and her mother are not slaves: How do they still fall under the slave system?

Alice
Greenwood and her mother are free slaves. Alice's husband, Issac Jackson is a slave, and after
Rufus tries to rape Alice, beats up Rufus. Alice and Issac decide to run away after the fight.
They are caught and Issac is sold to slave traders to Mississippi. Alice is beaten and enslaved.
While she is in enslaved, Rufus, who claims to love her, buys her and takes her home. He asks
Dana to nurse her back to health. He tells Dana to convince Alice to become his
partner.

Alice is horrified at the thought of being with Rufus. Dana tells
her that...