Does it need to be connected to the internet? At that age, I think you could get away with installing stuff locally that they could play with.
IMO you should create guard rails that you intend her to eventually understand and circumvent. Nothing is more empowering for a kid interested in tech than thinking they figured out how to get around the guard rails. Just make sure you can detect when it has happened.
Do something locally on the machine to block internet access. Maybe something as simple as turning off the network adapter. One day she’ll either learn enough about the system to remove the guard rails, or she’ll find other interests.