Ok, I have a few ideas. First though, I would have her seen by a cardiologist. She could have had a strep infection that went undetected and damaged her heart. She could also have myocarditis.
If she has had chickenpox before, you might check to see if this is shingles.
Here too, is another post about a young person with symptoms that have remarkable similarity to your daughter's:
Another possibility: Neisseria meningitidis (bacteremia and meningitis)
And I'll just throw out the names of some other issues you could check:
Paroxysmal supraventricular tachycardia
abdominal aortic aneurism
hypertensive heart disease
Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency