Glad to help you.
I'm sure your daughter is familiar with remote controls at home, so she will be at home with a remote control train set.

The new power pack for the LionChief set has no variable voltage control like the older transformers do. They have a fixed 18 volt DC output which is all the LionChief sets need. The hand unit controls the speed with electronics in the locomotive.
The LionChief sets will also work with conventional AC transformers, but you set them to maximum voltage and again, control the speed with the remote, not the throttle handle like conventional locomotives.
The power packs for the LionChief sets have a DC voltage output, but have no throttle handle to regulate the voltage for speed control. In addition, any trains with whistle or horn sounds would sound continuously with a steady DC voltage on the track, as it is a DC voltage that triggers the sounds on conventional locomotives run on AC voltage. Therefore, the newer LionChief power packs would not be suitable at all to operate conventional trains.

Larry