Actually, if both of you lose and maintain a healthier weight you both win, regardless of who loses more weight relative to whom. I've always felt that the idea of competitive weight loss to be be a bad, bad idea.
What if your co-worker loses thirty pounds while you lose fifteen? She'll feel great at having "won", you'll feel bad for having "lost". Losing any weight is a major acheivement. If you feel bad about not measuring up to someone else, there's an excellent chance you'll become discouraged and quit altogether.
You have come to right place for support. There are very many very smart, informed and supportive dedicated people around here. Ask questions. Post what you are eating now and ask for advice. Read threads in a few different subforums, such as the Weight Loss Support forum or the Food sections at the bottom of the list.
Good luck to both you and your friend.
I'm Tealeaf, and I approve of this message.
My weight loss site, with blog, before and after pics, recipes, tips, charts, and stuff. Annie Takes Off