Sindalla was abandoned to the wilderness as a youngling and spared by Lamashtu, the Mother of Monsters. Lamashtu taught her the secrets of the druids. Sindalla had a knack for assuming the shape of various spiders. This made her a very accomplished assassin.
She can access just about anywhere, gather secrets, sneak up on her targets, and apply her natural toxins, then leave before any alarms are sounded.
She has most resources at her disposal and uses them very effectively. She would be the worlds most feared assassin, but she makes a habit of silencing those who mention her existence.
After all, the most deadly blade is the one you never hear.