The age of the daughter is not a surprise--- the number of children who learn chess and happen to be 8 is actually quite large(and no I don't have a citation, this is anecdotal). However of that group the number who the next day or so invent fairy-chess with a Fisher(kind of) variation is probably pretty close to 1! Were I the father, I'd be enormously proud and more than a little stunned. Shaking that off, I'd begin to encourage this spark as much as I could...