It takes time for some girls to get there periods espeically if they are atheltic and eat right for the most part it will come though most likely, if you want be sure to inform her pediatrician when she goes for her annual check ups before schools starts again just to get a second opinion
I had my period when I was 16, my breasts developed before then. I wouldn't worry about it. My mom had her period much earlier. Also, this could make her feel like there is something wrong with her. I'd let it go. If she's 18-19 then maybe book an apt then.
If she is athletic, then it is very normal. There is no age when a girl automatically gets her period. Everyone's body is different. I wouldn't worry too much, as long as she is reaching the other expected developmental milestones. However, you, as the parent, are the one who knows your daughter best.
Hope this helped!