Magic can do anything, Samuel.
Rowena kept a library of journals where she documented everything she knew about magic. She knew most of the truth about God, enough to know "the game was rigged." She immersed herself in all forms of magic and creating her own spells became her way of keeping control. In order to protect her library, she hexed her apartment so that no one other than Sam or Dean could enter without dying. Sam and Eileen manage to locate her old library and take everything from her apartment to the Men of Letters Bunker.
- Resurrection Spell: When Mary was killed, Rowena created a spell that could transform a spirit to human. However, since Mary's soul was in Heaven, she never finished it. The spell was completed by Sam, who uses it to revive Eileen Leahy. Unfortunately, the spell could only be use once.
While translating the Book of the Damned, Rowena is seen writing her translations into a journal. She eventually manages to find a spell to summon Lucifer in Hell and warding sigils that neutralized his powers.
Rowena is seen updating her journal with her latest translations from the Book of the Damned. When Jack arrived to ask for her help in reviving Mary. She tells him about the latest spell she recovered from the book called the Magice Necromantiorum which could bring Mary back.
Sam and Eileen make their way to Rowena's apartment hoping to find a way to prevent Eileen's spirit from one day becoming vengeful. When they arrive, they find Jacinda's body and start searching for what she was looking for. Eileen passes through a bookcase and finds her most valuable items. Sam looks through Rowena's old spellbooks and realized that she, while she didn't have all the details, she knew the game was rigged. Causing her to immerse herself in magic to stay in control. A page from one of the books falls out and Sam inspects it. The page contains a resurrection spell that Rowena was attempting to create to revive Mary by transforming the spirit into flesh. However, Mary was already in Heaven at the time, so Rowena never used it. Realizing that he can complete the spell, Sam decides to use it to revive Eileen. Sam and Eileen retrieve the ingredients they need for the spell and stow them and one of Rowena's journals in the Impala's trunk when Jacinda's mother and her sister Emily banish Eileen and capture Sam.
Since Rowena cast a hex in her apartment to kill anyone other than Sam or Dean, the witch creates a voodoo doll to torture Sam in order to compel him to recover Rowena's library and use the resurrection spell to revive her daughter. Sam offers to use the spell together, however the spell will only work once as Billie prevents any spell that cheats death from working after the first use.
As Sam gathers her old library, he tried to convince Emily to turn against her mother so she won't have to revive her dead sister, whom she hated in life. Emily recognizes that Sam is lying and tortures him into cooperating. Eileen returns with Dean in order to stop the witches and save Sam, but the spirit of Jacinda begins attacking. After a drawn out fight, Emily is killed by Dean, her mother is hexed by Sam, and Jacinda's spirit is dispatched when Dean burns her body.
In the Bunker's bathroom, Sam performs the spell to make Eileen's spirit human again. All of Rowena's spellbooks, along with everything else in her apartment, have been recovered and added to the Bunker's library.
- Dean refers to Sam as Rowena's protégé, capable of casting spells via hex bags, implying that Rowena left her stash for him to inherit and use in their fight against evil. He is also capable of completing the resurrection spell Rowena created. Rowena said that Sam is close to a "seasoned witch" in 15.03 The Rupture.