I assume this roommate is asking for more than you are willing to pay/can afford/than your stuff is worth. Er, why is she asking for $$? For damage? For a partial's month's rent? Just to be a pain in the ass?
You may need to go the Small Claims Court route with this -- it probably what's called conversion. See: http://en.wikipedia.org/wiki/Conversion_
You can represent yourself in Small Claims, but be aware that there is a jurisdictional limit. So if your stuff is worth, say, $1 million, it'll be too high for Small Claims, but $1,000 is probably going to be fine and will fit with what Small Claims would be used for.