Thanks for your query.
sores in the mouth needs to be examined by a doctor to find out the cause and treat accordingly. Yes, a viral upper respiratory tract
infection can cause similar symptoms and with a blocked nose, the child will breathe from the mouth and can have a bad odour. Kindly ask your daughter to rinse her mouth with Listerine
at least two to three times a day. This shall give her some relief till you consult the doctor.
I hope I have answered your query to your satisfaction.
Wishing your daughter an early recovery.