Watercolours? My hat's off to you; your layering is divine, and your middle panel is exquisite, although their dejection in the last panel makes me want to cry.
I think the reason I disliked JKR's style so much is that she's a bit lazy with how she controlled her scenes. Frequently, she just laid 'it' out there and expected the reader to interpret what they will out of it. What I mean is her 'words' made us rely on an iffy subtext to discern the power of any scene. For fanfiction, that may be all right, but for mainstream, that's almost criminal.
This scene is one of those that could have been so much better, imho, and I'm so glad you chose to illustrate it because the scene, as she wrote it, was hopelessly flat. What I find truly ironic is that if she had just included those two sentences you have in your author notes, then this illustration would never have been necessary.