Minecraft LAN says Unknown Host when trying to connect?

My sister and I are trying to connect to a LAN world, and when either of us opens to LAN and the other tries to connect, it says unknown host. We're both on the same Wi-Fi and have never had problems with LAN before. We just added mods but we both have them and their the same version. Any solutions/ ideas?

Modding Minecraft may result in compatibility errors with LAN and other types of server hosting. Try again without certain mods.

Open CMD and run "ipconfig /all" on boh computers.
Whichever computer is hosting the server, use its IPv4 in the configuration file. Then restart the server, and give your sister the IPv4 to connect to. It's generally 192.168.1.x

Try a ping or a tracert from the connecting PC to the lan serving PC. This may give a clue. Make sure the address of the LAn is the same every time it is opened.