I was banded May 22, and went for a three mile walk the following morning. Though I was pretty tired afterward, it was no big deal. My stomach felt sore as if I had done a bunch of sit-ups, but nothing like you would expect.In fact, all of the other people the following morning were commenting on how little pain they were feeling. Now having said that, let me say that it is possible your sister might experience more pain than other people. Walking will be good for her, but she will probably not want to walk up steep inclines or go for really long walks. Also,my surgeon has us on a liquid diet for at least three weeks following surgery. The food thing might be a hassle in Yosemite, I don't know for sure. She will also have to avoid immersion in pools, hot tubs, and hot springs till the incisions have fully healed, to avoid infection. And last but not least. She should avoid lifting heavy objects or wrestling with any wildlife. If all goes like it should, she should be mobile, and just a little sore in the gut. Definetely do-able.