We learned recently that our nanny has been double billing us and the other family for two hours per week on a day when my child has an after school activity. She is supposed to be at our home, doing work around the house (like laundry, cleaning play areas) but instead has taken on the extra two hours with the other family.
This is a very big offense and very dishonest. I can't understand why you are even considering giving her a bonus when she leaves, let alone posting on a nanny board whether its OK to reduce it. Please do not give this nanny a great reference and omit this. Its not fair to another family who will be trusting you to be honest.