Minecraft pe: will multiplayer local Wi-Fi go to a random map or one of my worlds?

So my sister is going to get minecraft pe after i recommended it and i want to play with her over the local Wi-Fi and started making a house for her and everything. But then i thought what if it spawns in a random map, not my one. Will that happen?

You can either join somebody else's world(what your sister will do) or you can allow people to join your world(what you will do).

It will only play on a random world if that is the world you open before allowing people to join.