Looks like she knows what she is doing there and I hope she has continued interest in the trains. It's fun to spend time with them when you are both having fun and enjoying something together.
The young kids pick this stuff up pretty quickly these days. They are very good at figuring out the buttons and things and running trains. My grandson has never derailed or wrecked a train, I can't say the same for myself, he thinks it's funny.
One thing to watch for, the kids will probably use the 'Brake' slider. When I first got my Legacy system, my grandson was using it to stop the trains. The next time I would try to run a train after he left, nothing would move! Took me a while, but I finally got wise and know what to look for. I seldom use the brake slider, so I was stumped when that first happened, thought the whole system had died.