A LORA concept for the Doppelganger from the Monster Girl Encyclopedia. It may require some img2img to fix details, but generally places the characters properly when generating both the woman and the doppleganger. The model can sometimes confuse subjects, so either give it several tries or inpaint to fix.
Doppelganger and Woman Concept: doppelconcept, 2girls, duo, doppelgirlmge, short black haired girl, [INSERT SECOND CHARACTER PROMPTS], clinging, behind, expressionless, black hair, red eyes, short hair, black dress, size difference, red hairband, black tendrils, black tentacles
OG Doppelganger Alone: doppelgirlmge,1girl, solo, short hair, black hair, red eyes, black dress, puffy sleeves, red hairband, eye headband symbol, torn dress, black tendrils, black tentacles
OG Noblewoman Alone: noblegirl, 1girl, solo, medium hair, blonde hair, blue eyes, purple dress, bare shoulders, gold tiara, purple gloves, bangs, choker, high heels, pink fan, ponytail, gold trim, eye symbol, hand fan