Well people like nandini do exist loving and spoiling their own children and using others for selfish reasons but having little bit of humanity. I think nandini had some feelings for vk and even some feelings for ram but her greed and selfishness has destroyed her. If she understands ram's value and starts adoring him then she may change as a person but I guess it's too late. Don't know why but I want her to become positive after getting karma of her deeds and genuinely repenting for them
About the case I am sure she didn't kill vk