A new employee already has a Workforce account under her email, can she use the same email to access our workforce account?

Yes, your employee can use the same login credentials across multiple QuickBooks Workforce accounts. Just send the invitation to her preferred email address. When she receives it, she should click the link and sign in using her existing details, rather than creating a new account.

Let me know if you have further questions about managing the QuickBooks Workforce account.