She should have contacted booking.com by phone or on the online contact form after she realised her error with the email address. The original booking was still valid, how would booking.com be aware if a wrong email address had been used. This has happened to me several times with Ryanair, mistyping an email and then not getting my confirmation email, I promptly contact them to resend using correct email. I would say you won't get your money back on this but you can try contacting them and explain what had happened.