So in the novelization there’s a scene where Rey considers trading BB-8 with Unkar Plutt. It explains that she’s not perfect, she’s not a saint. She had been promised 100 rations. Remember, she’s used to getting a quarter portion. She wouldn’t have to work every single day. She might be able to do other projects. To relax.
However, in the end, she reconsiders the ethics and morality, partially because Unkar Plutt announces “Thats my girl”. It took her everything, but realizes thats not what she wants to be. She has the chance to better herself by trading a robot, something many people would consider not a person.
But for assorted reasons, including that BB-8 trusted her, made her confront Plutt. She called him out and walked away with BB-8, and knowing she still only belonged to herself.
“The Droid is NOT for Sale.”