Alraune, since she is a Alraune, her lore might be the same as all others.
"Alraune, are being with intense sex drive with no concept of love, created from the intercourse of a Mandrake, and a Witch"
Pixie, is the closest thing we have to a Witch, or a Horny Succubus, did something to a Poor plant.
The Other concept would be even worse.
"Blood and Semen of hanged men dripped into the earth eventually grew a Mandrake with an Intense use for love Potions, Witches would also use them for intercourse creating the Alraune"
So yeah all we know is a Witch probably banged a random Hole, or a guy died Ejaculating.