Yes, she looks like a mix. EE have those puffy cheeks. EE also have slate colored feet which indicate a blue egg layer. I can't tell what color your chicks legs are. Are they slate or yellowish?
Oh, by the way....if she is a cross between BO and EE, she may produce light green/mint green eggs. When you cross a blue egg layer with a brown egg layer, you usually get some kind of green egg. It sure will be fun to find that first egg!