Leaving aside whether that would work or not, do you think killing the "mother" who is loved and respected by all the girls will help you get the girls?
Of course not, not all the girls, unless Clara keeps going towards the craziness shes shown lately. More of that might flip the girls against her one by one.
Of course, my MC is pursuing Lemon, and she sure would be on board of the idea of killing Clara, ending her slavery that she is in at the moment. She is her unwilling maid, bloodbank and, lets face it, probably a sex slave aswell.
Clara has already taken the first steps towards the lifestyle of her own master, whom she despises. Apparently she doesnt even realise it. While neither Cora or Lemon are chained in the basement, they sure are slaves to her. Cora is addicted to Claras blood and hanging around the source just to get more. Lemon is being kept really close, basically with an invisible chain.
Its only a matter of time until there is a third girl in slavery, then fourth and so on if Clara keeps going this path.