This is a place to ask parenting related questions and get some insight into how to handle things.
Answer: Two things come to mind. First, that this child might have an older sibling or other older child that they spend time with that is often taking things away from her. If this is the case then just dealing with your own two year old is not enough. Second, she is exerting her ownership and assertiveness. Neither are bad traits and the time will come that you will value these as well. For now focus on teaching her to ask for what she wants. Return objects and tell her to ask the other child if she can have it next. It is important that the goal is for her to replace actions with words and not to get ownership right then, but for her to be able to delay getting what she wants. Say to her, “You want Bobby’s pail. I see he is still using it.” “Say to him, I want the pail next.” Then help her wait. You will likely need to tell Bobby that when he is finished to give it to her, but over time they can handle the whole transaction themselves.