Keeping New and Old Ipads
The easiest thing is to back up the old iPad to iCloud or your computer using iTunes.

Then restore the old backup onto the new iPad Air (you need to erase all content and settings to get the device clean for the restore).

When the setup asks if you have a backup, load that on the new device.


delete all apps and settings on the old iPad that should not be there.
delete all apps and settings from the new iPad that should not be there.


At that point, you can use the two separately. Look to perhaps turn off automatic downloads. At some point you can wipe the old iPad and let your daughter start buying her own apps or split things with a mix of the old Apple ID and her new Apple ID as well - you can mix purchases unlike iCloud settings.