Dd2 is like this, not so much the spying but she hides things, food for later she made herself sick by drinking milk that was hidden away but it's also rocks, paper hair brushes even my book! I have learnt if anything is missing to ask her. Hoping the food will stop as she was sick for two days. Right now all her winter clothes are missing as she wants to wear dresses instead. Glad it's not just us, as dd1 was never like this.