"YB AUVQ DUUACRQ" I've tried every rotation of Cesear and lots of frequency analysis and all I've been able to come up with is "I'm done goodbye". The girl who wrote it says this isn't the answer but it's all I've found. I'm fairly sure that if it is monoalphabetic this has to be the answer but I want to see if anyone can come up with anything else.
I believe the answer is, in fact, I'm done goodbye. It is encrypted in the following logical order: For each letter, shift it two keys left on a standard QWERTY keyboard.