When they approached the counter, and the sales clerk wanted to scan one of the boxes Eleven held, she backed away, pressing herself against Tony. She didn't understand the concept at all and thought the woman was trying to take the Eggos away from her.
Her eyes went dark, her lip tight, her body took a threatening stance. The only reason she hadn't thrown the woman across the store and into a wall was because she'd rammed into Tony, and doing so had been just enough of a distraction to disrupt her concentration.