Nanny salary question

Hi,

Our nanny currently works two days a week for 8 hrs a day, and three days a week at 6 hrs a day.  In her contract we give her 10 paid holidays (in addition to sick leave and vacation).  The contract currently says holidays are paid at the full day rate.  Do other people do this, or would it be standard to simply pay her for the holiday based on the number of hours she would have worked that day?  (We will be amending our contract soon for other reasons, and I'm wondering whether we should propose this change as well.)

Thanks!