Thanks! And no, it wouldn't be.
I'm a fairly accomplished seamstress, anyway, so a little Supergirl or Superman costume isn't really a stretch. With matching hairbows, she'll be the cutest Supergirl ever!
You can buy commercial costumes, too, BTW. But I've looked at them and they're not good enough or well-built enough to survive Evie playing in them. I'm hoping to put this off long enough that it'll still fit come Halloween, but I promise to post pictures.