Rowena got it. I mean, she didn't know all the details, but she knew the game was rigged. So this... Magic. This is how she kept control.
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 valuable from her apartment to the Men of Letters Bunker.
- Sanetur Acre Vulnus: The healing spell used to close the Rupture is documented in one of Rowena's journals which she leant to Sam to help her perform it.
- Resurrection Spell: When Mary was killed, Rowena created a spell that could transform a spirit to human. However, since Mary's soul was happy 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 used 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 neutralize his powers.
Rowena's translations from the Book of the Damned can be seen on the table while everyone discusses how they plan to lure Lucifer out into the open.
Rowena is seen updating her journal with her latest translations from the Book of the Damned. When Jack arrives to ask for her help in reviving Mary, she tells him about the latest spell she's recovered from the book called the Magice Necromantiorum, which could bring Mary back.
While helping Rowena with the Sanetur Acre Vulnus, Sam holds one of Rowena's journals which he uses to help prepare for his part in the spell.
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 a hidden room containing Rowena's most valuable items. Sam looks through Rowena's old spellbooks and realized that, while she didn't have all the details, she knew there was something going on with God, that "the game was rigged". This caused her to immerse herself in magic to order to feel like she had some control over her life. 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, they found out at the time that Mary was already in Heaven, 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. They are about to leave when Jacinda's mother and her sister Emily banish Eileen and capture Sam.
Since Rowena cast a hex in her apartment to kill anyone who enters 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, but the witch reveals that the spell will only work once as Billie closes any loophole that cheats death as soon as she finds out about it.
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 accuses Sam of 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.
Sam uses a spell from one of Rowena's spellbooks to transport himself, Dean, and Castiel into Hell, where they are greeted by Rowena herself, now the Queen of Hell. Meanwhile, Eileen feeds the spell bowl to ensure they return once they're finished.
Sam and Dean use the same spell they used to transport themselves into Hell while Castiel and Jack keep an eye on the spell bowl. When Castiel decides to send himself to the brink of death to find and consult with Ruby in the Empty, he leaves Jack to feed the spell bowl until Sam and Dean return from Hell.
- 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 or at least the closest the Winchesters had besides her.