Carrie Thompson was the half-sister of Robert Johnson.
In the Timeless Universe
After Robert Johnson was almost murdered by a Rittenhouse agent, he starts to head back to see his sister. Rufus Carlin and Connor Mason drive next to him walking, and find out this information. Mason tells Johnson things about his sister he knew, such as the fact that she owns a juke joint, and manages to convince Johnson he knew Thompson and that should Johnson come with them to reunite with his sister.
Later, Thompson does come to the bar and hugs her brother. Johnson speaks with Thompson in private at the bar.