To be honest, it sounds like your friend may have a bit of jealousy stored up. You are pretty young lady and I can only imagine how you will look once you get down to your desired size/ healthier weight....smoking hottt! So in order to make you feel guilty and to start questioning your decision about the procedure she turns it into a God issue...one of Satans old tricks.
God did not intend for use to be obese and live unhealthy lifestyles. So many people die from cancer, diabetes, and cardiovascular disease- all which are preventable if we make and choose a healthier lifestyle and you are taking those steps to ensure that you do no fall victim to one of those diseases. God have given us the tools to take control of our lives. We didn't just magically come up with the various different wls...no God revealed those things to His children in order to help us...just like the other diseases.
I am not sure if your friend is within her h/w ratio, but alot of thinner people are not able to understand the difficulties an obese person face on a day to day basis. My sister is small...has been all her life. She eats whatever she wants and does not gain a pound and when I told her about my surgery she didn't understand why I couldn't really stick to a weightloss plan and exercise. I wanted her to be happy for me that I was taking this serious step, but to her it is taking the easy out. I had wanted her to be there with me when I have surgery, but now all I need/ want is me and God.
Do not be surprised that your friendship may change as you lose weight.