Make Sure UPNP is enabled in your router. Should be by default but some don't somtimes. but also if you're connecting to LAN, she needs to type in your Local IP address in the address when adding the Multiplayer Server. I'm also going to assume she is within the same LAN network as you and she isn't at another building or something.
Open your single player game press ESC and hit "Open to LAN". after that. have her connect to your Local IP address. should be something along the lines of 192.168.x.xxx
Hope this helps.