Adding New Client's Account to Current Account?

Hello, I have 1Password where I have a Personal account and a Business account. My new client wants me to join her account. When I click the "accept invite" button, it doesn't give me a choice to sign in - only to register. Is there a way that I can add the client's 1Password account to my current 1Password? That way I won't have to sign in and out again. I'm on a MAC. Thank you!