Hi OP,
I have nurtured my own daughter through much the same concerns and feelings.
Young Minds is an excellent resource. Please check out their website.
Praise her for confiding in you. Reassure her that you see her, hear her, and will do your best to understand her. Let her know that you will always be there to listen to her, and she can tell you anything, anytime.
I found this on the web and it seems very helpful.
"Model and encourage self-compassion. Be kind to yourself.
Teens learn by observing, so model self-compassion by treating yourself with kindness and understanding, even when facing challenges.
Validate her emotions. Encourage her to pause and validate her emotions to stop engaging in negative self-talk.
Practice self-care by encouraging healthy habits like exercise, good nutrition, and sufficient sleep, as these can positively impact mood and self-esteem.
Help her view challenges as opportunities for growth and learning, rather than as failures.
Praise effort and perseverance rather than solely focusing on outcomes. Encourage journaling as a way to explore thoughts and feelings, fostering self-awareness and self-acceptance.
Help your teen set achievable goals, both academically and personally. Encourage breaking down larger goals into smaller, manageable steps. Acknowledge and celebrate her successes, and milestones, reinforcing her sense of accomplishment.
Foster positive self-talk and affirmations. Encourage her to practice positive self-talk and affirmations. Help her identify and acknowledge her strengths and positive qualities. Challenge negative thoughts. Help her recognize and challenge negative self-talk.
Encourage hobbies and extracurricular activities to explore her interests and passions.
Participating in activities can help teens develop new skills and build confidence. Extracurricular activities can foster a sense of belonging and community.
Promote assertiveness and teach her those skills. Get her to learn to express her needs and opinions respectfully, while also respecting the needs of others. Assertiveness can help her feel empowered and it builds self-esteem. It can help teens establish and maintain healthy boundaries in their relationships."
Teach her that she is worthy just as she is. Look at the website of Jamie Kern Lima, the author of a book called Worthy. She does podcasts too.
Help her to notice that comparing herself to anyone else is unhealthy and detrimental to herself. She needs to be her own best friend.
I hope all this helps, because I know how painful parenting in these situations is. You've got this Mama!