I don't know if this will work since you switched it from domain to workgroup, but you can try prepending the domain name to the username with a backslash, like this:

User name: girlfriendsdomain\girlfriendsusername
Password: girlfriendspassword

Sometimes in Windows NT authentication, if you have a screen where the domain name is not available as an entry field, you have to prepend the domain name like that.

Of course, it would only work if she's actually connected to the work LAN. You can't do that unless the domain in question is really there.