You can find another way/place to store your food that would be more out of your reach. You can consider complaining to authorities that manage apartment/roommate issues. OR…
To all the foods in your pantry, attach post-it notes with “friendly reminders.” For example:
**
“Tut tut tut. God is watching when your roomie isn’t”** 
**
“Haaaaw, Baysharam, Bayghairat, Bayhayaa, Chori karti hai.”
**
**
“Your theft (petty as it is) is being video taped. Will be sent to apartment authorities…and America’s Saddest Home Videos”**
Place hidden cameras. If you catch her, you can use the evidence as blackmail.