I second (or third) Terry Pratchett.

Robert Asprin might be a good choice, either the Myth books or the Phule books, but you might want to read them first to be sure. I have a sieve for a memory, and don't tend to remember adult situations when recommending books for small children.

Has she read Lemony Snicket?

I would also highly recommend Shakespeare's Star Wars.

The Phantom Tollbooth would be good. It's full of dreadful puns.

Possibly Artemis Fowl, though they aren't as loaded with absurdity.

The Night they Stole the Alphabet is pretty silly.