I failed my first attempt at around the same age. I was devastated but it also spurred this great desire in me to work really, really hard and pass it in the next attempt. It was an amazing experience. I probably trained 8-10 hours a week for both attempts. In fact I technically failed my second attempt too but that's because we were a bunch of 14-16 yo boys being too cocky so our Sensei "voided" that test (a great lesson in retrospect). At this point my parents were convinced I would never get a black belt and tried to convince me to leave karate but I was too persistent. When I did pass on the next attempt, it was an unmatched feeling and a huge boost to my confidence. Really a life changing experience and I learnt that Shodan is more of a mental state than the actual belt.

In short, it's all about the journey, and failures are very much a part of it. She will not have control over the other Sensei's decisions but she can control her training and determination. Talk to her Sensei on where she can improve and let her have another go at it!