Hey, Just a quick Authors note.

Uzushigakure was not destoryed Until After Kushina had Naruto.

Mei is Naruto's Little sister.

When Kushina was visting her village with Naru who was only 4 years old. 

Kushina then went into labour and had Mei, then Mei vanished into thin air. 

Then about a year after Kushina had left to go back to the leaf village, Mei was found, and taken back into the village. 

Then four years later, the village was destroyed, leaving Mei an 'Orphan', and she went wondering for two years, before finding cousin Karin, staying in the Hidden Grass village for a year. 

Then Cousin Karin left for the Chunin Exams and Mei went looking for her. 

Thus Ending up outside the leaf village a year later, where she collapsed. 

The last thing she saw was a woman running towards her with long crimson red hair, wearing a green apron with a white dress underneath.

That's all, just an explanation of Mei's past.

Sayonara!

-SarenaiNamikaze