Treasa is a well known ranger of the Cragmaw Forest. She is often seen selling fur in communities all around the area. and It was she who discovered the lost mine while looking into a Night Goblin
problem in the area.
Update: The party found Tresea in Cragmaw Cave, already half consumed by the goblins. She had been captured with Thrag Grandaxe and Magni Borirson.