Hi.. Thanks for the query.. Yes, it is true that if she has a dry mouth she can have a false feeling of having a coating on her teeth.. But it would not be actually present.. So the first priority is to treat dry mouth for which you need to get the exact cause ruled out. Treating the underlying cause can help in resolution of symptoms.. The basic treatment is the same what she is given but if it still did not work then medications like Pilocarpine can be advised as it will help in stimulating saliva flow and relieve dry mouth.. Also once get her teeth cleaned by scaling procedure to check if she finds any improvement.. Hope this helps.. Regards..