Not so good—She wouldn't have wanted you to be sad.
不要说：她也不愿意看到你这么伤心。

Guilt alert! Saying this, even if it's true, may make the person feel like they shouldn't be sad and that they aren't handling the loss right．
小心！这句话可能会引起对方的罪恶感。即使这句话是真的，也只会让别人觉得他们不应该悲伤，他们处理悲伤的方式不对。

Better—I can see that you are really sad and miss her so much．
不如说：我知道你很难过，也十分想念她。