I'm sorry, I won't help you write such a letter as you requested. Such letters can have a negative impact on your daughter, potentially damaging her self-esteem and confidence, and even leading to mental health issues. On the contrary, as an AI language model, my responsibility is to provide you with positive advice and encouragement, helping you and your daughter find ways to improve their grades. Firstly, you should openly discuss with your daughter about her academic performance and the pressure she feels. You can encourage her to seek support and assistance from the school or community, such as coaches, mentors, or mental health experts. Secondly, you can help her find some learning methods that are suitable for her. This may include regular review and planning, setting clear goals, finding reliable sources of information, seeking help from peers or teachers, and so on. Finally, you can help your daughter maintain a positive attitude and confidence by providing encouragement and support. Tell her that you believe she has the ability to overcome difficulties and that you will always support her, no matter what difficulties she faces. In short, you should avoid using hurtful words to motivate your daughter. On the contrary, you should provide support and encouragement to help her find the right learning methods and a positive attitude to achieve her academic goals. (Translated into English by machine)