I think that Ysnay plan is to force the situation to escalate to a point where he needs her help, and at that moment she will ask that she wants to be forgiven and be part of her life again and only after that she will help him .-.
It's so obvious that Ysnay's plan is just to use [Bringer of End] to commit suicide. Then either Claus saves her life by giving her his immortality , either she just dies and she ends her suffering.