Every day for the past week my house mate has woken up, come down stairs and into the kitchen to make food in the middle of the night (around 3am). My bedroom is right next door to the kitchen (you have to go through the kitchen to get to it) and I hear EVERYTHING that goes on in there and I'm a light sleeper, so she has woken me up by preparing full on meals all week, I joked about it to begin with but now I've had enough. I got up and told her it was an issue and she just laughed, and when she realised I wasn't joking any more she said it wasn't her fault that she got hungry, and no she couldn't take anything to her room before bed because she'll just eat it even if she wasn't hungry, no she couldn't eat before she went to bed, and it's my fault because I chose the room next to the kitchen In the first place; by her logic I'm the one at fault for waking up when she decides to microwave herself some peas and curry sauce to go with her waffles at 3am.
I don't know what to do about it, she does this every time I try to talk with her when she's taken something too far, she has absolutely no respect for me or my things and if I try to address it she brushes it all off as a joke. I'm tired and angry; I've had enough but I don't know how to make her listen. I don't want to end up hating her because she's a close friend, but she's turning out to be a bad house mate.

How about switching rooms with her?

I pay the most because I also have a study and en suite and I don't want to give them up. There's no way she'd swap; she couldn't afford it.

I'm not sure what all that en suite and study involve but teacherjenn had the most appropriate answer and if you can't do that (switch rooms) then switch beds only, for just sleeping hours.
I have had episodes of getting up to eat in the middle of the night off and off for about 30 years. I am convinced that it is a habit that can be broken pretty easily. I found that if I resisted the urge to eat because I was so " famished " at 3 AM, when I got up at my normal time, say 6 AM-- I wasn't even hungry enough to eat breakfast. Where did all that extreme hunger go? It is just a nasty habit unless she had a medical condition that causes it. It's a will power issue (usually). If she is obese or diabetic it may be a medical issue.
Sleep deprivation is a means of torture. It will get worse if it continues.
If she won't cooperate after you have exhausted the options (such as switching beds only) you need to make new housing arrangements.

You are a light sleeper, and have anxiety issues and as irritating as that is some ear plugs at night would help you greatly I feel.

Swapping is impractical due to the contract we signed and pre-dated cheques already sent to our landlord and so on. I'll look into earplugs, I've tried them in the past and found them uncomfortable but that was some time ago; thanks for the suggestion.

It sounds like she is the one with the unreasonable attitude. There has to be a way that she can have something in her room to eat so she doesn't wake you. What are your schedules like? It appears she may be home during part of the day while you are working. It sounds to me that you are willing to make some compromise but she seems dead set on just doing what she does no matter what you feel.

It's the other way around actually, she's out most of the day while I'm at home. She needs to get up earlier than I do and she often uses her workload as an excuse or a way to argue against me. She works more than I do but not more than everyone else we live with. (There are 5 of us, she treats them just the same; she has used all of one of the other girl's tupperware and hasn't washed or returned them in a week, despite being asked to do so repeatedly.)
I'm getting to the point where I want to buy dry food for her that she can keep in her room but I can't afford that.

Well if she is like this towards all of you, maybe a meeting with all of you is in order. Why should one person make everyone else miserable.

How big is the study? Can you put your bed in there?