You can't change someone's make-up beautiful.
I'm lucky. After reading all of that. My housemate is "tidy" but not clean.. I can't recall the last time she picked up a hoover or mop. She did at the inset through "guilt" as I started cleaning but then stopped. I took over, just decided I want a clean house and that's it.
She moves things of mine, doesn't put them back, pinches my food for her mates while I am away and doesn't replace, drinks my coffee, leaving hers because she knows she's going to run out of hers, thinks I don't know They are small things but annoying because I refuse to pay for her stuff, her "rent" is for utilities and her room, I threw in evening meals, after all I cook anyway..
She just hides in her room when she's totally stuffed up.
So for me, I at least have the house the way I want it, I "pretend" I'm on my own still that being, I would have been doing that if she wasn't there, just a tad more than usual".. And, same, doesn't seem to like taking the garbage out, water the plants haha.
With your flatmate, she's dirty/lazy and dis-organised full stop.
Firstly, you should have a roster, and you should be telling her, listen no offense but we are sharing this place, so the loungeroom needs to be turned back into a loungeroom or else we aren't going to get along which will cause a situation of having to go back to the way I had things, on my own... No offense but I can help if you like, perhaps you need a few cheap storage boxes and shelving, to give you more room, in your bedroom... And, we both work so let's work out a small roster, nothing major, I'm not Hitler (laugh) but something that gives us a little equal time out for ourselves huh...
I think if she realises that it may mean that you two separate from this situation she may look at things a little differently.