I first asked her what brand of paper she was using, (that can make a HUGE difference). Student brands most often will not react the same as the professional grade papers (my personal preference has been 300 lb CP Arches paper and for exercises 140 lb). Student grade papers have a tendency to curl badly and blending color does not react the same way due to the surface.
I asked: how old her was the paper ?
Her reply: about 10 years old.
The problem is: depending on how long and where the paper is stored, overtime the elements can degrade the sizing on the surface (yes even though it is archival). Most likely you won't notice anything wrong until you apply water and color, then the big reveal happens. You start to see blotches and spots or even scratches. It's truly a shame, after you have spent good money for good paper and especially frustrating if you have taken time to create an intricate sketch. Usually the fresher the paper, the better the results.
In my students case, the paper immediately soaked up the all water and color, acting more like a blotting paper or paper towel, making the technique ineffective. What you are looking for is the water and color to stay on the surface while your working and have the ability mingle giving that transparent watercolor look.
The exercise below can help you create a luminous washes and gives you better understanding of the feel and flow of water with color that I'm looking for.
140 lb Cold Press Arches Paper