How is it going with the roomie?? I was reading this and thinking back to my roommates that I had in the past, and unless it was milk, butter, things like that, we stuck to our own food that we bought. If we had a dinner party or something, then we'd shop together and split the cost, but other than that, we ate what we bought. Now, my 3rd roommate was a little different, but that was because she had other issues as well. She would take advantage of what she could (like not paying rent, utility bills, and she was also a drug user and alcoholic... it was SO much fun!).

I hope your roommate will show you some courtesy and, unless you both agree to share the food and you eat her things as well, then she needs to stick to her part of the fridge. Otherwise she's just being manipulative and inconsiderate.