My stepdaughter is still stealing food?

Okay my stepdaughter (12 1/2 yrs old) came to live with us a few weeks ago because of some issues she was having with her mother (she doesnt feed them often, never spends time with them, etc) so the 12 1/2 yr old was acting out in school and got suspended for fighting for the 3 time in one yr.....anyway since she has come to live with us I've done everything to try and make her feel more comfortable even making up a closet hideaway for her for when she just wants to get away...her and our 5 yr old daughter has lots of fun together but the closet was for when she kinda just wants to be alonge.....when she first got here I noticed she was taking food and hiding it in her hideaway and when I go to clean up I find the empty container or wrappers...I've told her that whatever she wants to eat she can have it..... now she seems to be getting a lot more comfortable but almost a month later and she is still stealing food and leaving the nasty wrappers in places food should not be because I think she forgets their in their...what should I do without making her feel uncomfortable?