In the late 1500s, after Tomasin White surrendered her soul to Scáthach and thereafter became known as The Butcher, Priscilla was among those sacrificed in the name of the ancient gods. Like others before and after her, her death was believed to appease the bloodthirsty wrath of ancient deities, and in exchange for the murder of innocents, the Roanoke colony would be allowed to prosper in their chosen land under the gods' protection.
Personality and Appearance
Before being seen herself, Priscilla was originally thought to be figment of Flora's imagination brought on by her parent's divorce. Upon Flora's disappearance, Priscilla was believed to the fearsome ghost of a child due to Cricket Marlowe's reaction when he heard her name. However, Priscilla's appearance is that of an innocent colonial child. She wears the same dirty, long nightdress-like gown in which she was sacrificed. Her hair is ginger and pulled-back with a single braid going above her face. She has pale skin and blue eyes.
When Flora came to visit Lee at the house, she often disappeared and was found in the closet. She told her mother that she had a friend named Priscilla there, but nobody saw anyone inside.
After Flora disappeared, everyone immediately thought that she was captured by The Butcher and the rest of the colony in order to make the Millers leave. However, when Thomasin appeared during Cricket's seance, she explained to Lee that her daughter had been taken by Priscilla in the hopes of protecting her from the rest of the colony, herself included.
When Elias came back to the house and heard that Priscilla took Flora, he immediately said he could help and took the Millers to her favorite place to play. Going deep into the woods, they soon saw a whole gang of ghosts and disturbing figures including Priscilla and Flora. While trying to talk to Priscilla, horns echoed around the forest, an unknown tribe came and killed Elias with their bows and arrows which made Matt and Shelby run away.
Later that night, enchanted by Scáthach, Matt went to the underground chamber nearby the house and left Shelby alone in the house while she was sleeping. When she woke up and started looking for him, she saw the colony coming to the house carrying torches. Afraid, she screamed his name and he came. They saw Flora in the hands of The Butcher. Priscilla then appeared and hit the Butcher in the head making her let go off Flora, who then ran to her uncle and aunt.
When the Polks bring Shelby, Matt and Flora back to the house to be killed, the Butcher intends to kill Flora first, angering Priscilla as they made a promise that she'd be killed last.
Priscilla killed a willing Lee so she could stay with her to protect her from The Butcher as a promise to Flora. 
This marks Savannah Liles's, Estelle Hermansen's, and Audrey Casson's first appearance on AHS.