Kindly answer these questions. 1.Is it foam or saliva? 2.Does she have good oral hygiene? 3. Does she have fever? Children usually have salivation at night. It aggravates if she has associated nose block or she is a mouth breather. It also happens if she has poor oral hygiene. Brush her teeth and use a mouth wash before she goes to sleep. If no fever I would not worry too much about it.
Foam could just be drools.