If you agreed to pay your nanny a weekly $300 for 40 hours, should I have to pay my nanny more for working and extra 7hours because I’m getting emergency surgery?

Instead of arriving at 8am, she’s arriving at 5am and staying till 8pm, instead of leaving at 4pm

We agreed to a set amount per week but she says she deserves more pay if she’s staying longer.

How much more should I pay her? That seems ridiculous