hello,
i think you should take her to the doctor, i remember my friend in high school was late we had our period at 11..13 and she became 14 and still didn't had her period and she still look like a kid so afterward her mom took her to the doctor they give her an injection some kind of a hormone then she had her period and every thing went back to normal even though she is still tiny but now she is married and she have kids. i hope there is nothing to worry about but you need to take her a s a p to the doctor. don't waist your time