Little sister getting bullied

Cryslin • Mimmy of two beautiful babies and married to the love of my life!
My little sister who's not so little is 14 and 5'11… so as some of you know if your not 5'5, 100lbs and perfect, kids at school make fun of you. I got bullied in middle school too so I know what she's going through, but my question is how can I help her she cries everyday doesn't wanna go to school and has a very low self esteem . I reassure her all the time that she is beautiful but she doesn't believe me. She tries to be nice and make friends but they just call her fat, ugly, says she looks like a tranny and everything else. I'm scared of what the isolation and depression could do to her, so what can I do to help? Any advice? Sorry for the lengthy post 🙊