It sounds like either a firmware bug, or a corrupt file on the device messing things up.
are you sure the trouble started out of the blue? Or might your daughter have added a new file/document just before the trouble started? Or, might there have been a firmware update just before the trouble started. whichgrep
seems to suggest the latter.
If it's the firmware, you could downgrade back to firmware version 2.1.5. You can find the link to this firmware in this
thread. Note that manually up/downgrading firmware is not officially supported by Kobo. Also, a newer Touch model might use the Glo firmware instead of the Touch firmware. Loading the wrong firmware can break your Touch. So you have to be sure which firmware your specific device needs. (See the same thread for more info.)
If you don't think the problem is due to the firmware, you take all your documents of the Glo, and load them back one by one. Start with the ones that you know have previously worked. If, after processing a new document, the problem re-occurs, delete the last document you added. If that solves the problem that was the/one of the corrupt files.