Looks cool
To be honest I don't mind watch the show and I actually prefer Fluttershy out of all of them as well. This piece here though is very good.
The background is simple yet looks chaotic as well since it is mostly dark colors being used here to paint the scenery. Then comes the pony which you did by hand. I agree with you that a radioactive symbol is not very creative but let your mind expand a bit and I am sure you can come up with a much better looking cutie mark here.
She actually looks pretty cool. Kind of laughed at how her name is a pun on Yuri as well. This piece was pretty cool.
Overall, another pony OC I see here.