When you go to meet your friend, dress yourself up in your favorite/finest clothes - or maybe even wear something new. Take charge of your beauty and wear every extra pound with pride - allow your inner beauty to glow. I'm quite sure your friendship was never based on how you look anyway.
If you happen to notice that look of disappointment in your friend, it will be an opportunity for you to tell her how hard it's been for your self-esteem. It might reduce the risk of her saying something stupid. After all this time, I think everyone should know losing weight isn't as easy as following a simple formula or diet plan.
Good luck - let us know how it goes.