No, you need to be in range of the target clients. It works by spoofing the ap's mac and sending deauth packets, if you arent in range of your target, they wont receive the packets.
EDIT: just reread your post, (mdk3 mon0 m -t "her routers mac address") I dont know what the m option does, I thought you typed d, but I assume from the way you explained it that you are deauthenticating the clients