That looks just the right sort of thing to do - it's fun, silly, and instructive all at the same time. As long as s/// is approached simply at first it shouldn't be too difficult to introduce and can do fun things. I was planning on something similar to start with. You could probably do something good with splitting a sentence into words and then printing them out in random order - introducing split, lists, etc. Then perhaps have a hash that holds replacements for words etc...

The only thing that concerns me is the lack of graphics as I'm not sure how long simple word games will hold her attention. I might look at doing something with Tk - perhaps create a very simple interface that lets you do things with colors and text, it should be possible to package away most of the complexity - I'll post it if it works out.