two weeks out and weight gain is this common?

my friend had a revision two weeks ago. which she had her bypass revise to where it was when she got the surgey 8 years ago. on her first visit one week later her total weight loss was 18lbs. whi*****luded the weight loss of the liquid diet a week prior to the surgery.she weighted herself today and said her weight is 4lbs up. what is going on has this happen to anyone before. 

Make sure she is weighing first thing in AM, after peeing... Also, is she eating CARBS? PROTEIN is all she should be doing... Is she exercising? walking? anything like that? Perhaps she is retaining water from pain meds, etc....

I had my revision two weeks ago yesterday and conintue to drop. Currently I am at 26 lbs down.. I have noticed that if I don't walk and drink my fluids that I do not drop.. but if I am consistent on the exercise and fluids i am dropping a 1/2 to 1/ 1/2 pds a day. Is she drinking her fluids and walking?