it seems she's on purpose deviating your instructions despite you have told her your requirements. Perhaps she has already known very well you need her to babysit your kid very much. Now it seems she is the boss, not you.
Be firm on your ground, no compromise. If she can't reach your hygienic standard, fire w/ no mercy.
I can't tolerate anyone handling food and handling kids with such dirty habits. It directly affects everyone's health in the household.