Well, I have to agree with Johanna....(Which some here thought they would never hear!! Old news now, right?)

However, since you are looking for an answer...I once read that you can take a 5' tall woman and assume 100lbs. Add 5lbs to that for every inch over 5 feet. So at 5'6" that would be 130lbs. She can eat out if she wants to eat lots of salads or grilled chicken and probably not gain weight. Scrambled eggs don't take much time to make, nor does peanut butter on toast for breakfast or a snack. I guess it all depends on her activity level...does she exercise? How far does she walk each day? Maybe suggest that she get a pedometer...? It never hurts to add more fruit to her diet...this time of year apples are plentiful, filling and portable.
If it were ME, I would just suggest that she go walk around the mall a few times and on the 4th pass, buy some new clothes that fit!!
I hope that helps a little!

Duncan and Jennifer