Could Breathlessness Be Due To Pneumonia Or Mitochondria Disease?

Hi my name is Lina, my little niece has mitochondrial disease, she 2 years of age, at this time she is in the hospital with a touch of pnenomia, she is having a hard time breathig, is it because of pnenomia or is the mitochondria is getting worst. please help me understand this. thank you, lina