The word order used to describe the travelling party mentions the Levite first, then his donkeys, and then his concubine. She is mentioned after the donkeys. This may be simply coincidental, but in light of the previous verses, it is not a stretch to conclude that the narrator wants us to see that she was but a servant of his, just like the donkeys were.
10 But the man would not spend the night. He rose up and departed and arrived opposite Jebus (that is, Jerusalem). He had with him a couple of saddled donkeys, and his concubine was with him.