My fourteen year old daughter fears she might have breast cancer. my sister says she is too young to have it, is she correct?

Too young: Hormonal influence is most common cause of breast pain in a teen. An ultrasound can provide reassurance and check for cysts or other benign non cancerous growth

Not likely: It is very,very rare to have breast cancer so young. I recommend you take her to a breast specialist or her pediatrician. The bigger concern is why is she having these ideas at this age: is there someone close to her that has breast cancer? Did she hear someone talking at school? It is important to find out or have your pediatrician speak with her. See my others posts on breast pain/fibrocystic