Originally, she didn’t want the shine on the hand claws either, but she changed her mind at the last minute, making the tail the main difference.
Here is a Rainbow Dash dragon form.
This pic is a variation of this one, which is the one published with a fanfic chapter.
Deviantart link: Dragon Form Master Mev
Derpibooru link: https://derpibooru.org/images/2593345
I have every intention of this picture being the last variation I post for anyone noticing the other two around the same time.