We tried deactivating her old square account but she still can't sign up with my business account. We need her to access square appointments dashboard.
HI, you would need to setup Team Management and Custom Permission Sets. Her individual account should not have anything to do with your business account.
Square Support Pages
https://squareup.com/help/us/en/article/5591-get-started-with-employee-management
https://squareup.com/help/us/en/article/5822-employee-permissions
Square Community