Hi Jaun... A very nice size two there....
I think your girl is young and hipless like many of us used to be...lol. I would say she is underweight and well air-brushed... but nicely proportioned. At least she doesn't have a gargantuan chest spilling out of that top.
If you check out her arms they are very, very slender. She has very little developed muscle which would also add to her small weight. If she were to pump herself, and have a ripped body she could easily gain 10 to 15 pounds and look even smaller.
Which would be healthier as added muscle allows for a higher calorie intake and thus is more nutritionally sound. So do heavy cardio workouts. Cutting down on food often times leaves the body looking tiny and healthy but in fact may not be feeding the organs the required amount of nutrient to function at their optimum level. That leads to problems as the body ages.