Here's how to get there:
1. Talk to Samia: You'll find her at the entrance to the Central City area. She'll ask you to find her sister, Aisha, who went looking for a legendary artifact.
2. Travel to Windmill Isle: From Central City, you can reach Windmill Isle by using the Windmill Isle Portal. You'll find this portal in the west side of Central City.
3. Find Aisha: Once you reach Windmill Isle, you need to explore the area and find Aisha. She will be in the northern part of the Isle near a lighthouse.
Important Note: You need to progress through the game enough to unlock the Windmill Isle Portal before Samia will ask you to find her sister. Make sure you've completed the earlier stages of the game and unlocked the necessary areas before you reach Central City.