How much to pay nanny who will be babysitting multiple kids

Hello! My nanny who babysits my three kids for me will be babysitting my friends‘ kids as well while we all go out on a date night. I’m genuinely curious how much we should pay her because I have no idea how this works. When I asked her how much she would like to receive she said she will be fine with whatever we give her so that’s no help.

I pay her $24 an hour for my three kids aged 6, 4 and 3. In addition to this she will be also watching two 6 year old boys (my son’s best friends) and a 14-year-old daughter who does not really need watching, but will be joining them in the house. So the total will be five kids, not counting the 14-year-old.

What is a fair amount to pay her? There are three families total that will be paying for this. There will be no bedtime responsibilities. We are going at 3 PM and plan to come back around 7 PM.