Alan has taken the words out of my mouth. Can you confirm which zones were purchased for the travelcard? And has your daughter travelled outside those zones by train? If she has then the card will have tried to deduct the extension fare from the PAYG balance. If there was no credit then the balance will now be negative and that means that the travelcard is invalid.
There are some hidden gotchas in the system, so if you can’t see what the issue is can you paste the recent journey history here and I’ll see if I can spot anything.
In the meantime, if she tops up enough to put the balance back to at least zero then the travelcard will work again.