The ghosts of Bly Manor are bound by certain rules and limitations, but Viola’s story sets a precedent. The Haunting of Bly Manor establishes that an especially stubborn soul can cling onto the mortal realm via something physical – in Viola’s case, the chest of treasured belongings and the manor itself, which she fought so hard to keep. If Viola could manage this supernatural feat, Dani might’ve done the same, and the most treasured thing in her life would, of course, be Jamie. Just as Viola remained attached to the mortal world via Bly, Dani’s ghost could be stubbornly fixed to Jamie, or if the idea of using another human as an anchor seems strange, Jamie’s engagement ring.
This would explain the mystery hand comforting Jamie in The Haunting of Bly Manor‘s final moments. The ambiguous scene can be viewed in a variety of ways. Perhaps it’s nothing more than Jamie’s imagination, or a metaphor for the couple’s enduring love. Taking the scene at face value, however, Dani’s ghost appears to be watching over Jamie in secret. The only way this would be possible within The Haunting of Bly Manor‘s rules is if Dani’s soul was connected to Jamie. And more than just hinting at Dani’s presence, the hand also alludes towards a posthumous reunion. If the ghost of Dani lived on, she could create a gravity well around Jamie (or the engagement ring), and the only soul that would be caught would be Jamie’s. Therefore, once Jamie dies, her soul will become trapped within Dani’s gravity well and the couple can finally be together again in corporeal form.
Eventually, Dani’s ghost would transform into the faceless, forgotten husk that many other ghosts became, but The Haunting of Bly Manor doesn’t reveal how long this process took. Peter seems to believe it’s happening to him after only a year, but Viola died centuries before the main story and her transition seems to take far longer, perhaps because she’s the center of the gravity well. Dani would only have to wait another 40 or 50 years to be reunited with Jamie, which may be short enough to avoid losing herself. After finding each other in the afterlife, Dani and Jamie could then move on together, meaning neither of them would suffer the indignity of becoming a faceless denizen. Based on how she ends her story, Jamie certainly believes that Dani will forget her, lose herself and wander Bly as a ghost, but the hand on her shoulder in the final scene flies in the face of this, suggesting Jamie is incorrectly assuming the worst.
Some might also question why the spectral Dani wouldn’t show herself to Jamie, if the hand was indeed hers. The Haunting of Bly Manor tacitly provides an explanation for this. Should the ghost of Dani appear to the still-living Jamie, the gardener would do exactly what she attempted to do during her final trip to Bly manor. Instead, Dani would want her soulmate to live her natural life, which is why she only emerges when Jamie is asleep.