This must be rough for both of you. The term croup refers to a heterogeneous group of mainly acute and infectious processes that are characterized by a bark-like or brassy cough and may be associated with hoarseness, inspiratory stridor, and respiratory distress. Croup typically affects the voice box, windpipe, and airways.
Croup generally occurs in the age group, 6 months to 5 years. What you describe casts doubt on the diagnosis, as by age 8, most children have stopped having croup. Some croup is viral; another form is deemed to be allergic and quickly responsive to even a single dose of high dose steroids.
It would be important to confirm that your daughter's illnesses meet the usual criteria for this diagnosis. Other chronic respiratory diseases such as cystic fibrosis (CF), asthma and bronchomalacia could be confused with croup.
Your best bet at this time would be to seek a second opinion, consultation with a pediatric pulmonologist, also know as a lung specialist, who, with a fresh perspective on her illness, might conclude that your daughter's illness is actually another respiratory disease.
Good luck.