The elven healer may be encountered during the side quest A Healing Hand. Corporal Vale mentions to the Herald that the refugees at the Crossroads are dire need of healer, and suggests looking into finding one that can be of assistance at Redcliffe Village. At first the Healer is reluctant to except the Herald's request as she feels that the people at the Crossroads will not welcome an elven healer. After a little convincing the Healer will reallocate to the Crossroads and can be found in one of the local homes.
Hinterlands Healer will ask the Herald for assistance in gathering certain types of herbs in order to treat the injured patients:
A Healing Hand
A Common Treatment
An Advanced Treatment
A Rare Treatment