Maybe the story of Bella and Edward in 'Twilight'. Bella was a teenage girl. Their love story was considered great in the sense that it was a love that crossed the boundaries between a human and a vampire. Edward was attracted to Bella's unique scent but also fell in love with her personality. Bella was drawn to Edward's mystery and charm, and they had to overcome many obstacles, including the danger that Edward's vampire nature posed to Bella.
It could be anyone! Maybe it's a rising star or a familiar face in the entertainment industry. The lack of further context makes it difficult to identify exactly who she is.
Common signs can include excessive sadness, withdrawal from friends and family. For example, she might stop going to social events she used to love. Also, changes in eating and sleeping patterns are often seen, like eating too much or too little, sleeping all day or having insomnia.
Encourage her to engage in activities she used to like. Maybe she liked dancing. Sign her up for a dance class or just have a little dance session at home. Also, make sure she has a healthy lifestyle. Help her with having regular meals and proper sleep. And most importantly, let her know that she is not alone and that you are there for her no matter what.
It could be many characters. For example, in 'The Hunger Games', Katniss Everdeen is a teenage girl hero. She volunteers to take her sister's place in the deadly Hunger Games, showing great courage and resourcefulness in the fight for survival against other tributes and the Capitol's tyranny.