My roommate eats all my food. Out of spite I accidentally I commented poorly on her "I'm getting fat" comment. What should I do?

Today I was going out to get two boxes of pizza so that I can eat them over the course of the week and freeze the rest. I told her just this, and then asked her if she wanted anything and she said no and that I was getting plenty of food. Next thing you know were back home and she basically gobbles up a whole med pizza to herself, when I only had 2 slices.

I was snoozing on the couch when she comes downstairs, gobbles up 3 more slices before work then lifts her shirt up and says "these pants are getting too small for me" and boy was she ever right. Out of spite I commented back saying "well maybe if you didn't eat all that pizza..."

I know that was a bitch move. Shes pissed off at me. I really don't want to apologize but then again I don't know how to apologize.

Reddit, what should I do?

Edit: She does this with everything! I'll ask her if she wants anything before I cook or buy something and she'll say no. Then she'll grill me on how unhealthy my meals are even if I buy/make a caesar salad, then she'll be the one eating all of it at the end of the day.

Edit: She just came home and I could tell that she was over it, so I didn't apologize. However she went straight for the box of whatever was left of my pizza on my shelf said "I'm always hungry after work" and ate two more slices and acted like nothing was wrong. UGH! I can't stand her!!! Worst part of all this is that me and her are pretty good friends. Were the most civil out of all out other roommates and I don't want that to change. I want to be on good terms with all of them. I know if I told her to stop she would get offended.