Encanto: The lost Madrigal and the Stranger

It's now 6 months since Mirabel have save the miracle from her family.

But one day Mirabel act completely weird, and went often in the jungle and not just that. One day found the little Antonio something, and then he find out like Mirabel and Camilo that the Madrigal's have a lost family member Willow Madrigal.

But what they didn't know is that Willow is still alive and just far away of them.

What happened in the past ?, why isn't Willow by her Family, why did she left ?,and what for a secret have Mirabel ?.