The compression artifacts really detract from the image. Since you're so far under the file size restriction (just over 80k, and the limit is 150k) you probably could have eliminated this by reducing the compression at the camera (low/fine compression) or when saving this after editing. I like the composition, but the spot on the wall and the specks on the ground are a bit distracting. The girl's bright clothing contrasts nicely with the drab background.
My questions about this image are, Why do you title this image "Yellow Shirt"? Is the shirt the most important element of the image? Is the title you decided on, souly for the purpose of this challenge? If so, why not title the image "Left Shoe"? Or "Sock" The Point I am making is that if you choose a title it should have something to do with the main point of the creation. Here it is obvious that the little girl is more important than what she wears.
Meets challenge Description........10 (I believe the description is more about Isolation than mimimalism)
Meets the definition of Minimalism..10..(the way you framed this images seems to me to gives me more insight about the girl.
Technical..... 8 for the most part I think this image is fine except for some electronic artifacts the can be seen at the base of the wall.
Artistic.....10 The framing of the vents in the wall really add something to this image.
Average score..................9 Nice image needing a little bit of work on technical. Nice job and I hope you are in the running.
This would be better in black & white (i know i know, but you could change the title, too). :)
Also, the angle at which you took this is kind of tragic. I see that you are standing to the side a bit so that she's not in the center of the photograph, but you should still aim the camera perpindicular to the wall so that the line where the wall meets the ground is horizontal and so that she's sitting completely vertical -- The way you took it means that if you rotate it a few degrees to straighten up that line, she'll be tilted a little bit.
Where are all her friends? I love the grey backgroun with the bright colors in the girl. Nice choice with the yellow shirt and pink socks. She feels so much smaller with that mass of gray.