What really matters in this scenario is what is right for you. You are doing what you need to do to take care of yourself, and it is totally your choice to share or not to share such personal information.
I am scheduled for VSG on 9/15 in TJ, and only my parents, my son, and my brother know about it. I have yet to tell any of my friends. I may or may not after the procedure, i just haven't decided what i want to do. It has nothing to do with feeling unsupported or being concerned about others reactions. It just a very personal decision that i made after a very long period of consideration, and i still have my own feelings to sort out. For me, right now, i need to look after my own emotions, deal with the major changes ahead for me, and even though i am very secure in my decision to do this, i am still feeling a little overwhelmed by all of it. I don't really want to add the extra emotional energy, good or bad, to my plate right now.
You can be honest with your friend and tell her that you're worn out after your trip and would like to pick up the next week.
The definition of friendship does not include a "share all" clause, and a true friend who really loves you would understand your need to do what is best for you.
Good luck and i hope you are doing well!