Reference letter

I have been asked to write a reference letter. Was thinking of writing something along the lines of: XX has worked as my assistant for 5 years. After 2 years she was able to take over the whole department so that I could leave for greener pastures and pursue my own career. Or as our boss phrased it. She was the one doing all the work while you did all the partying. She has slight control-freak qualities, and left alone she will bury herself in work, sometimes forgetting there is a life to be led. But somehow I don't this this'll fly :)...Will have to rephrase it slightly...