So yes, I'm a fan of Cult of the Lamb. I adore the game, and like so many fans, before official canon came along, I came up with my own interpretation of the Lamb. In my personal lore, Diana (My name for the Lamb, who I see as female) was eventually flushed out of hiding and caught by the Cult of the Old Faith due to a plague Kallamar spread to kill her village. She fled, even as everyone she knew was dying, but already been infected, making her easy to capture and bring before the Bishops to die.
As per canon, she was beheaded and revived by The One Who Waits to make a cult and free him, but Diana didn't come back fully restored. Kallamar's plague had taken its toll on her, and though she opened her eyes and cut down her executioner... Her world was dark. The plague had taken her sight; she was blind. Naturally, a blinded vessel would have been worthless to her Master, so the Red Crown became her eyes. Anything its singular eye could see, she now could, though her vision was now forever tinged red.
So then why is there a lamb wearing the Green Crown there? Well, that's the second half of my world's lore! As Diana defeats the Bishops, you normally get to put them on a pedestal as a trophy. I find that boring. In MY AU, the Crowns grow enamored with Diana for having the strength and power to kill their respective Bishops, and claim them for herself. This leads to the other four Crowns occasionally smacking the Red Crown aside and planting themselves atop her head, causing dramatic changes in Diana's appearance and personality.
Should the Green Crown take Diana over, she becomes more wild and 'unstable', as the Green Crown is the Crown of Chaos, much like how the Red Crown is the Crown of Death. And yes, her Cult has to deal with the side effects each Crown has over their Great Leader... Stay tuned, as I have one for each Crown and a bonus piece where I'll go more in depth about what each Crown lets her do!