The man that Valerie Hobson knew as 'Father' had been a student of Manfred Wallace, who had secured the notes and journals of Victor Frankenstein. In addition to the fallen creator of reanimated life, which he applied to his own experimental procedures. Manfred had an interest in reconstructive actions that put him literally decades ahead of any other medical doctor, such as the rudimentary basics of reconstructive surgery and transplant surgery. He had been experimenting for over a decade when he found Victor's journals in a small bookshop in Dublin, a forgotten part of an estate sale. Victor's copious notes on over coming rejection and mating flesh from multiple sources.
He immediately started experimenting on cadavers, going slow as he honed his understanding of what Frankenstein had done. Slowly he looked for better and better 'donors' to see about making the perfect human as he dove into the darker sciences and then alchemy. Then SHE was brought into his source's morgue. Her brain was dashed in and her trachea was crushed but other than that SHE was a perfect start to his experiment. He made her 'average' looking due to the massive rebuilding of her face and throat, figuring he could work on her appearance over time. The scars where he put in an intact brain (from a murdered girl) and rebuilt the crushed skull were hidden under her hairline and once lightning restored her to living breathing life he introduced her as his 'niece' come to live with him after a terrible train accident had killed her parents and left her without a shred of her old life. That was when things started getting .. odd. Her strength, agility and healing factor were unprecedented and she took to the martial skills of fencing like one born to it.
Very rough, wasn't sure how you'd like it to fit..and how much 'slayerness' she retained.