If some obvious triggering event didn't bring this on, might be good to get a whole body/health work up, just in case it is something new and not concussion related..

[makes it hard to regularly push her limits as the doctors suggest]
If she can find the line of no symptoms increase, then don't push past it..
Let your body tell you when to move forward with activities..
Doctors don't always know what is best for each person..