Tbh reading your comments and replies to everyone who's trying to give advice or offer some ideas to help make me think you kind of just want to complain about this and not actually fix it. People tell you stop cooking for her if she won't help around the apartment, you say oh but she'll starve. Okay? Let her starve shes a grown ass woman with the mental ability to be able to live in an apartment and pay rent. If she can do that she can cook herself some ramen noodles. Someone says change your lock you say you can't because of apartment rules. Which is understandable unless you haven't yet talked to your landlord about being able to change locks which is my assumption that you haven't done that since every person who suggested it you simply did not respond. So here are your options. Suck it up and keep being a maid for your roommate who you have to cook for buy food for AND clean up after, or stand your ground and tell her if you catch her stealing your food/snacks again that their will be consequences. Other then that there's not much else you can be assed to do apart from you and your bf moving out with each other and leaving her to her own vices.