All of the below is theory and conjecture crafted by players.
Lebel the Celebrant
Little is known of what Lebel may have looked like. She was a treasoner at one point, but revealed her own to the Assembly. Middlemost/Characters/Nashandre says she was kind.
Background
Lebel was described as a "treasonous celebrant" and "pacifist" with a heart of gold. She hails from Chronicle, potentially, but even this is unclear.
She was the lover of Holland the Itinerant and a friend of Middlemost/Characters/Nashandre. The latter she knew through their mutual collaboration as treasoners.
At some point she was taken by the Assembly during a trial and turned into a horrific creature meant to serve them.
Is it possible Lebel was the Groundskeeper?
Discovery
We first found Lebel's name when discovering her rifle, but we believe we met on the very first step of our journey. She killed us. Threw us into that pit.
But it wasn't her anymore. It was whatever the Assembly made her.
The Groundskeeper kept Holland's body close, but did Holland ever meet her?
Later we found a note and evidence of Holland in Chronicle, in the middle of plague district. We believe Lebel was rescued from Chronicle, and originally came from the city damned from memory. She escaped Chronicle. If that's true then...
Then Yonmarl wasn't alone. But is that what happened?
Was Lebel from Chronicle?