@process Well... MUDs are still around. It's not my project but I've been following a codebase called CoffeeMUD for many years. The code quality is pretty meh but it's decades old, still in active development, and has pretty much every feature you could want. You might get her started using the in-game editors which can do a lot. It's open source, so when you were ready you could move on to code. Multiplayer, so you could work on it together. It's an idea anyway.
@process I know my 5 year old nephew is starting to get into Minecraft. In another few years when his reading is better I was considering trying to introduce him to how to write mods for it.