I can see having a human around for things that need to be done by a human but never understood in the Swedish original, the book, or the remake why the human was needed to hunt for the vampire. Clearly Eli\Abby is stronger and as such completely able to hunt. Maybe in her feral state she might not be great at disposing of the bodies, and that might be where the human is also needed, but to go out and kill victims opens the vamp and human up to unnecessary risk and, as in both versions\novel, exposure. Seemed off they (the human and "daughter") had not been found out already, especially in the modern age with police work, forensics, becoming so advanced. Getting away with killing people is no longer as easy as it was!