She has had a few situations at school where other kids have mentioned there not being a tooth fairy. I have been able to answer these questions as what the other child's parent said was not specific to there being or not being a fairy, just they would have to decide how much their child would get from the fairy.
Email Concern with kids at school telling her first.
Stick to your story Phyllis...half the fun is the bit where they sort of know its not all true but mum and dad are too stoopid to have worked it out. I told my 11 yr old if she didnt' believe the tooth fairy wouldn't leave her any money...made it worth while her playing along and keeps the fun of it going.