Local Minecraft server isn't working?
Added (1). It was working the other day, me and my cousin use the same Wi-Fi and everything but it stopped working for some reason and her world won't show up for me to join anymore. It's not because of the devices, I don't know why.
Added (2). URGENT! Local Minecraft server isn't working
Are you connecting via an external ip or local host? You connect through to your server through an IP address, which is essentially a password to let you through. Naturally, these change over time, so simply go into google and search 'what is my ip', copy the ip and replace the current one.
To make it even easier, as you're connecting to your local network, just replace your IP address with 'localhost' (without the quotes). This means that you can join your server without ever changing your IP.