nano 4g behaved strangely after charging on dock

My grand-daughter's 4th generation nano started to develop lines on the screen when she removed it from my Acoustic Solutions ipod speaker docking station. The ipod is only six months old but the lines on the screen developed from one or two to masses and eventually turned into white screen. Does anyone out there know what the cause could be? She knows that she hasn't dropped it or been careless with it in any other way and at twenty years of age has no need to fib! As a pensioner I'm not really up to date with problems but I do have a 3g, 4g, and a classic but I've never come across any problems when using them on the docking station.