If you haven’t taken the Meteorite to Two Island yet, you’ll need to finish that quest first.
Deliberately fall through the ice on the north side of the first floor of the cave. Climb back up the ladder, then purposefully fall through the eastern piece of ice in the new area. Slide down the ice then climb up the ladder. After climbing the ladder, fall through the southern piece of ice. Skate up, then right, then down and then fall through the ice again. Get the Waterfall skill and teach it to one of your Pokémon. Go up the waterfall in the previous cave using your new skill, and then go down the ladder to find Lorelai.
The signs will show the direction you need to go. To solve the maze, go Up → Left → Right → Down.
