How easy or hard is to convert from OPT (valid F1 status) to F2 within USA?

Hi, I am currently on F1 student visa at University of Kentucky (UK). I have recently obtained PhD in Toxicology from UK and my optional practical training (OPT) will start from August 16,2012 and valid until August 15, 2013. I already have a job offer in the same department. My wife is currently on OPT and she would like to convert her visa status to F2. She is currently working at UK with legal F1 status (on OPT). We would like to know that if she applied for F2 status change, does she need to stop working right away or she needs to keep working while her status is pending with USCIS for F2?