I haven't uploaded a picture of my Fluttershy, have I? Technically, I really can't. They'd all be mature... Super mature. Her body is overly exaggerated.
Technically, it kind of takes place of the way how the show goes. Not exactly the same, but certain scenarios in that show pretty much happened in this different dimension. Fluttershy here is a hybrid of a bull(father) and of course, a Pegasus(her mother). Just like the show, she didn't have the greatest child-hood (that we know of)... Buuuuttt, this one would be a little more darker. She also has a sister a swell named Blind Smiles. Who, she hasn't seen for a long long time due to a certain event.
Never been sure on her design as a kid though. Very short for her age, or tall? Same with Rainbow Dash. I kind of messed this up, making them look older/taller than I actually wanted.
This also takes place before them receiving their cutie-marks. One thing for sure. Rainbow Dash has pretty much always protected her from being bullied for such a long time, felt like the only one who showed any care for her. Even if she was weak. Fluttershy wanted to grow up to be like her, do anything for her. She wanted to repay the favor, being very loyal to her... Try to (if her fear of course doesn't get in the way).