Sharra the Healer is a member of an Eldathyn retreat that is not what it seems.
Location[]
She stands in the small room reachable by entering the temple compound, taking the first turn right, and then immediately entering the door on the left.
Background[]
She appears human, and acts like the healer of a retreat for followers of Eldath, the good-aligned goddess of peace and tranquility.
However, 
she and all the other "Eldathyn" there are actually yuan-ti in disguise, and the "retreat" is in fact a secret temple dedicated to the evil snake god Sseth.
Interaction[]
You can talk to her to bring up her temple services (Healing, Donate, Identify), or to let you safely rest.
When asked about the Heartstone Gem or happenings in Kuldahar, she claims not to know anything.
Once the hostilities break out in the monastery, Sharra attacks you on sight like all the other Eldathyn.