SSH public key not Working - No supported authentication methods available
The safest way to convert to openssh format without introducing a typo is to have her open her private key in PuTTY's "puttygen" graphical utility. At the top of the dialog box should be a textbox labelled "Public key for pasting into OpenSSH authorized_keys file" which does just what it says.
Alternately, on your system, use ssh-keygen's import option
$ ssh-keygen -i -f file_to_convert > output