Some view it more of a freak out thing, and others not so much. For myself, I would always cough up more than a couple tablespoonfuls. Only once did I have a very prolonged bleed that was scary. Concerts = a ton of smoke. Also her blood pressure probably spiked due to the concert/excitement/being in the mosh pit, etc.
I was having issues with high blood pressure for a while, and after going on avapro for high blood pressure, my bleeds greatly decreased. After seeing what a much lower blood pressure can do with bleeds, I now believe our lungs become structurally compromised over time due to chronic infection and other issues with CF. If the venal system in our lungs (capilaries, vessels, etc) are compromised, and we have a spike in blood pressure (exactly when I had bleeds...After sprints, sex, etc), we can have bleeds. Keeping my blood pressure very low via changing my diet and being on meds for it, has helped to so far totally eliminate my bleeds. I still have occasional streaking, but that is rare and only after long exertion.
Sorry for rambling, but the point is bleeds and your response towards them are based on the amount, duration, frequency, and also the individual patient. They can be caused by so many things. Smoke/pollutants, infection, spike in blood pressure (as explained above), etc. She herself should know if it's serious or not, and depending on her age and maturity, should respond accordingly.
I wish her the best, and I hope she responds appropriately.