How would anyone deal with this situation?

Alright, 3 days ago I brought 4 cartons of soda drinks, a Variety of, Coke, Sprite, Fanta and root-beer. Each cartoon has 12 cans. My roommate says, she doesn't drink any soda because " It's not that healthy." I put them all in the fridge,The day before Yesterday I had one sprite.So there should be 47 cans in the fridge at least, but what I saw in the fridge yesterday was really less than 40 I counted them, and I found them 35!!!. I was walking out of my room and her room door was opened, I saw that she has like 10 0r more!! How do I deal with that?! And is this stealing?!