I agree with Zetacatty.
Your sister loves you and doesn't want to lose you, not that she will of course.
My husband and mother were the same.
Although my hubby was supportive he did have a little cry one morning and admitted it was because he didn't want to lose me. I explained that the chances of losing me to a weight related illness was much more likely and the wls was my last chance after a lifetime of yoyo dieting.
My mum made it quite obvious that she was against the surgery, she too has battled with her weight for most of her life and is now crippled with arthritis. She cried on the morning I left for my surgery as if she would never see me again, but you have to be strong and after reading as much as you can you are very unlikely to have made the decision to have surgery lightly.
We have all researched and researched some more because we know it is a life changing experience not just for ourselves but our families too, so the best thing to do is prepare yourself and be able to answer all your sisters questions and fears.
Good luck and remember she is probably worried about you.
Wendy. xXx