I signed up today and logged in immediately after getting the confirmation email, so either they fixed the problem or your sister misread the email, Jankinonya.
Crumbpicker, your friend's email server has probably sent the confirmation email to the spam can or the trash. It happens. Have them check their spam folder if they have not yet deleted it, or just have them re-sign up.
If it was some kind of error they have likely cleared it up as I signed up and in ten minutes was posting.