Just be like a stone that remains in the water for centuries and only gets wet at the surface and remain totally dry inside and all your worries shall disappear. Hopefully:)
Luckily I had nice flatmates, we had separate rooms and attached baths, only shared living/kitchens in uni .
it would have been a serious issue like this if the two girls werent that nice. cuase we (4) guys never used to clean the dishes, well I have done it some times, but Katie and Laurain were too nice!
so the year i spent there went guite nicely!
after uni, i bought a house, and got two of my desi friends to share it.
now one is very clean, the other one never used to clean or do anything.
I still remember his fridge having expired milk, and 2 years old cereals in kitchen aaaaaaaaaaahh when he was living at other place.
but here we made some rules, every one do kitchen, bathrooms, and other living and beds hoover etc. turn by turn.
dish cleaning.. if someone clean it early then he has to wash up less, otherwise he will get the punishment to clean the whole,
he has changed himself very much, but whenever it comes to him, we usualy delayed by atleast one day! ;) and then he get some bashing from me and other guy cause we are quite frank and friendly we do that with no offence.
so if she is your friend then ask her gently, if not then leave her things to her, its pitty you have to share bathroom as well. cause you cant do much about it to change her habbits. just make her realise ... it was dirty..etc.
hope it will work, but i doubt it very much if she didnt change in 8 months how could she be changed in few more months.
but atleast show your displeasure about this.