You need to ensure the end pin (the support below the cello body which rests on the floor) is on a surface where it can't slip. Otherwise, the player will get into bad habits because you can't hold the instrument in the correct playing position and move your hands and arms freely at the same time!
So whether you need one of this type of device (you certainly don't need both) depends mainly on the floor covering where she is going to practice at home. If that is a carpet or soft floor where the pin can "stick in" without slipping, you don't need one. If it's a hard wood or vinyl floor then you do. The most portable devices use a chair leg to anchor the support, so they can be used anywhere (the cello is played sitting down, of course).
I assume the school itself will have suitable flooring for playing there - otherwise the device wouldn't be considered an "optional accessory" but "essential".