[quote=ImportantNobody]
Evvie randomly slips on the water and knocks you out of the danger zone. Plus it's obvious her tail could divert the electric flow from the rest of her body if it went through her feet. (scientifically 100% accurate)
[/quote]

The only way to do that would be to knock him over the cliff before Arthur launches the attack (since pretty much the entire plateau is covered in water now). And like Goldeagle said, the electricity is specifically targeted. Evvie could be standing directly between Arthur and Gregor in a three foot deep puddle and she still wouldn't get touched. The normal rules of electricity don't really apply, so long as Arthur has a conductive surface to transfer through.

There's also the problem of Evvie being next to Arthur at the start of the fireball attack, and nowhere near Gregor. She'd have to be actively trying to save him from an attack no one knows is coming in order to reach him in time to avoid the electricity.