... a couple of weeks ago I knocked myself out when I was drunk and they had to ring an ambulance as I couldn't stand up and was throwing up all over myself ...
You're a tit for drinking that much. And to all those people who are saying "you're a student, why shouldn't you drink so much that you fall unconscious and nearly get yourself into a state where you need your stomach pumped" (or words to that effect), I feel sorry for you.
... whilst on the same night one guy that went to the same club as me on the same night went missing and was eventually found dead in the river - she semi-blames me for his death because 'that ambulance could have been saving him'.
Yes, this is unreasonable, but you're hardly being sensitive about it. Sounds like you had more than enough to drink to warrant an ambulance being called (unless you really think it's normal to be unconscious and throwing up all over yourself?), and frankly, there probably WAS something better that ambulance could have been doing.
Anyway last night she was initially having a go at me for that, usually I just sit there and take it but last night I just said 'look, move on with your life, everyone else has'. Error.
Yes, that was nice of you.
Then she came out with this tirade of stuff she'd obviously bottled up for ages. Apparently she thinks I'm the most selfish person of all time because I don't wash up for a day or two...
Well "selfish" is a good word for that. Immature on her part to bottle it up and not just say something to you about it, but maybe she has a point on this one?
... that I'm horrible to another of our flatmates even though I'm really not ...
You sure you're not? One person's "teasing" can easily be another person's "horrible". As above, would be better for her to talk to you about it rather than drunk ranting though.
... and best of all, that I'm gay for her boyfriend when we're just quite good friends and get on pretty well. This isn't helped by the fact that when they called an ambulance he had to shower me to get the sick off me. She's very naive and thinks any male contact is massively gay and a big nono - even cleaning my sick when I'm semi-conscious.
OK, that sounds a bit over the top. Point to you. Sounds like you're lucky to have a mate good enough to shower your own stupidity off you!
To top this all off, apparently she rings her parents every week to have a cry about me being such a horrible person...
She sounds very sensitive. It's nice to see you're being so understanding about her feelings. (Yes, she's gone about telling you the wrong way, but your response sounds just as bad.)
Anyway this is uni accomodaiton so I've gotta live with her for one more week now and then the whole semester after Easter - it's gonna be SO awkward, what do we think I should do? When we're both in the kitchen it's just gonna be horrible...
Talk to her, clear the air, have an adult conversation? Apologise for being a ****? That would probably make it all less awkward.
EDIT:
From your "update" post later in the thread, sounds like she's been the man - she's apologised to you for her behaviour. Have you considered reciprocating that apology and, as above, having an adult conversation?
Just my $0.02. Sorry about the lack of "smash her pasty" etc.