Hilde is one of Griff's thugs, she is also the Scoundrel merchant for Fort Joy. She will attack you if you begin a fight with Griff. You'll find her hanging around Griff's Kitchen and the Shrine to the Seven, usually walking back and forth to and from.
She sells the following skill books..
Adrenaline, Chloroform, Sawtooth Knife, Throwing Knife and Vault.
WARNING: If you fight Griff and his thugs, Hilde is apart of that group, meaning if she dies there will no longer be a Scoundrel skill book vendor in Fort Joy.