I know that the first reaction in this case would be to think of Dcm as very disrespectful towards you, and your private space, but actually, she might not even realize that she is crossing the line.
You need to lay it out straight, and now " Dcm, I don't mean to be disrespectful, but parents and children, are only allowed to be on daycare grounds that's been approved by Licensing.
(unlocking a closet? seriously?
)