When Jenny says that Robin brings love “down to a level,” she means that Robin degrades love and doesn’t revere it the way Jenny thinks she should. To Jenny, love is sacred, and one person should never hurt a person whom they love or who loves them. This is ironic, considering Jenny is trying to take over Nora and Robin’s relationship—violently, in this scene. Jenny wants to seem like the victim in this situation, but that is difficult to do since, from Nora’s perspective, Jenny must be a villain.