Nah, I don't see why. Art isn't a school report you don't want anyone to copy from. Or at least my stuff isn't. I'm more concerned about these people's morality than I am about them stealing my artwork. I mean even if the picture they posted recieves good feedback, both I and they know it's really for me. (So...yeah, I guess that's another positive side to this whole deal - the appreciation for your artwork gets spread without it looking like you're crying for attention. Also...watermarks are annoying as all fuck. They always look like pretentious self-advertisements.)
I really liked what you did with the hair coloring on this, her hair is very vibrant and helps her stand out! The dress isnt too bad but I am more of a fan of smooth/shiny dress types personally, but I suppose it works with what design you were going for. Also, how exactly does a pony walking on all fours also carry around a parasol?
I've made one for also Rainbow Dash, I've made for the other Main Six too, I just haven't coloured them yet. As for the others....meh, the only BG characters I did a dress for are Celestia, Bon Bon, Derpy and Lyra.