This is purely anecdotal, but I'm a female, and when I first got serious about getting healthier and losing weight a few years ago, it literally took a couple of months before I saw the needle on the scale move significantly in the direction I wanted it to. It's not unusual for my weight to fluctuate by 3-5 lbs in any week. I think a lot of it is water weight, but I've even weighed myself before and after exercising (which usually consists of running anywhere from 3 to 7 miles) and weighed more after exercising than before.
Depending on the time of year, I'm down anywhere from 15-25 lbs from where I started (when I finally decided to lose weight, I was between 150-155, I bottomed out at 127, and I typically hover around 135, give or take a couple). I prefer to be 135 or less. When I exceed that weight and put for the effort to lose even just 2 or 3 lbs, it typically takes at least a month for the scale to consistently reflect my efforts.
As others have said, it takes more than a week to see results. If she puts forth consistent effort and still hasn't lost anything after 6-8 weeks, then I would start to worry.
Also, as a side note, at 5'6", I really have to make a concerted effort to keep my calories (after accounting for exercise) at 1200 or less if I want to lose weight, and that's even with running 20 miles a week and going to a group exercise class 2-3 times a week.