The biggest tip-off to me is that if someone was 
going to make a fake cel of that scene, they 
would have included her armor. If you look at the 
spellcasting sequences frame by frame, you can 
tell that the armor is done on a separate layer. 
And to the best of my memory, she's always 
wearing armor when she uses her magic, so you 
won't ever see this exact image on screen. That, 
combined with the points Misha made, make the cel 
an unlikely candidate for a fake. I have a 
similar bank cel of Fuu which has the same 
problem, no armor, and until someone gives me 
hard evidence to the contrary, I'll believe that 
it's real.

Skorp