Hello there ,
Thanks for writing your query,
According to your history i suspect your daughter has developed lesion on the floor of the mouth which may be caused by obstuction of minor salivary glands or SUBLINGUAL glands .
Such cystic lesion is called RANULA
It is a swelling of the salivary gland duct on the floor of the mouth underneath the tongue because of trauma,stone,blocked salivary duct.
So i will suggest you please visit to and oral surgeon as soon as possible and get the thorough examination done and take a proper treatment.
i hope this helps ,