Same as wolf said it packmentality . They are hiding it to save for later.
She's just being instinctive. That's what her ancestors, wolves, sometimes do. A pack does this (but usually they bury it) when they do not want any other animals to eat their prey. When they are ready to eat again, they dig up the meat. Hope I was of help!
She is afraid you will be an Indian giver n steal her treat back off her she mustn't trust ppl very much lol