My granddaughter's frenulum is too so short that she can't touch the roof of her mouth. is this condition harmful?

Potentially: This condition can, in some cases interfere with feeding or normal speech development. Many times nothing needs to be done but when the condition is causing issues there is a simple, often office based procedure called a frenulectomy or frenectomy that can be performed. I'd recommend you speak with a pediatric ENT doctor for more information. Hope this helps

Maybe/not: The frenulum under the tongue has a variable length at birth and tends to stretch out some with age.As long as the kid can get the tip of the tongue over the bottom teeth it is unlikely to cause a problem forming words. It is more an issue when it forms a heart shaped dimpling when the tongue sticks out. Feeding difficulty is one of the few reasons for early treatment. It can be cut back if needed