We recognize her as the Hester from Chapter 1. The beautiful, attractive person who is not afraid to show her hair and not afraid to display her beauty. The sunlight, which previously shunned Hester, now seeks her out, and the forest seems to glow. Dimmesdale has also come back to life, if only for a short time, and he is now hopeful and energetic. We have not seen this from Dimmesdale for a long time, and most likely will not see it ever again.
Puritan society can be harsh and crippling to one's inner self.
Hawthorne created the forest to give the characters a place to escape and express their true thoughts, beliefs, and emotions. It was here that thoughts and ideas flowed as endlessly as the babbling brook, and emotion was as wild as the forest itself. There are no restraints in the natural world, because it is just that, natural. No intrusion from people means no disturbance in the natural order, and therefore serves to bring its inhabitants away from their world, and into this older one.