How to join minecraft LAN worlds?

She has to click the "Open to LAN" button on the menu, then it should show up for you at the bottom of multiplayer. You also have to be on the same network, other wise it won't work.

When my kids were trying to connect with LAN, it turned out that my daughter had to allow the connection through her firewall settings.

You don't direct connect. She is supposed to press esc and open to lan, then you are supposed to click on multiplayer and at the bottom of the server list (or your screen, could be there too) should be a lan server with your ip address on it, since it's a lan server.

Make sure both your sister and you are using the same exact version of Minecraft. Also, make sure both of you are using a vanilla profile without any mods installed. Also, make sure both sides have allowed Minecraft through All their installed firewalls on the PC. If not.

Okay, try this.
Both of you download Tunngle: http://www.tunngle.net/index.php?l=en. Create an account and login. Create a private lobby by accessing the "Community" tab.

Whoever is hosting, click "Start" on your computer (the windows icon at the bottom left hand corner of your screen).
In the search bar, type in "Run".
Click on the program that says "Run".
In the address bar, type in "ncpa.cpl" and hit "Enter".
Look for the network adapter that says "Tunngle".
Right click it and select "Properties".
Look for the line that says "Internet Protocol Version 4 (TCP/IPv4).
Double click on it.
Click on "Advanced".
At the bottom where it says "Interface Metric", change the value to 1.
Save and close.
Now, run Minecraft and click "Open to LAN". This should cause a port number to be broadcasted in chat.
The person that connects to the server run Minecraft and click "Multiplayer" and then "Direct Connect". The host needs to provide the connector with their Tunngle virtual IP address as well as their port number. The host can get the IP address via the bottom left hand corner of the screen. The connector needs to input the values like this <IP Address>:<Port>. I'll give you an example of the format: 1.1.12.34:50242.

Just what Zachary Swanson said, Make sure you and your sister on on the same EXACT internet or Wi-Fi. Then have your sister open to LAN in the "Esc" Menu. Then you (not your sister, she stays in game and waits for you to join) go onto the main menu and click "Multiplayer" then scroll down to the LAN world your sisters world is on and ENJOY.