Brief Answer:
May be due to the vitamin deficiency

Detailed Answer:
Hi,
I have gone through your query ; it suggests that your daughter may be suffering from the vitamin deficiency such as B complex or folic acid.
But to rule out other disease she may go for
1. Oral examination by ENT specialist or send me the image of the palate.
2. Serum vitamin and minerals level and
3. Check, if any change in toothpaste or oral cavity related cosmetics.

In this condition most of time multivitamin capsule treat the condition very well within a week, if the condition persist after this then better to go for above mentioned protocol.

Thanks

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Brief Answer:
Yes, It is possible to have a canker sore that does not hurt.

Detailed Answer:
Hi,

Apologize if my previous answer wasn't clear. To answer your question, yes some canker sores are asymptomatic. It starts to hurt only when it comes in contact with an irritating agent such as spices, salt and acidic foods. However if the sore is completely painless even when irritated, it needs to be evaluated for presence of infection including STD.

Hope I am clear now.

Thanks

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