This has not happened to me, but I would definitely send an email letting her know that you do not have an open door policy, especially when the daycare is closed and that in the future you would relaly appreciate it if she could knock or ring the bell. I wouldn't make it confrontational, just a friendly email to let her know. Maybe end it on a positive like "have a great two weeks and I look forward to seeing you and *** when we get back". As it is the first time, I would treat it like that. If you make it too confrontational, she will get defensive and things may get worse. Now, if she does it again after you have told her, that is different...then I would be giving her a warning of termination.