The idea is not mine, I've just came across this request and found it very funny. Just imagine their dialogues:
— I can grant your any wish.
— The Great and Powerful Trrrixie can any wish better than you, silly weird squirrel!
— But I can make you a magical pony
— Trixie already is the most magical pony in Equestria!
This fits my headcanon Trixie perfectly.
Trixie's design here is from this merch vector: Trixie Lulamoon vector
, I loved that additional piece of mane and how the light strokes look there.