You could let her dive into unity :), but maybe that would be to much,
I was going to say that. Unity can be as simple or as complex as you want it to be.
I'm not much of a realtime guy but I had to deliver a fairly large project in Unity recently and I found it quite a nice mix of simplicity mixed with option of roll-your-sleeves-up-and-start-coding customizability, much like any mature application. (It was also quite a novelty to present the finished product to the client without having to render or comp.)
But back on the topic, I would imagine that a 10 year old could get into the free version of Unity with very little trouble.
-Eric
