Geez, could it be some underlying medical issue? An hour to struggle with breathing hard is quite a long time.
Has she had any indepth testing done to determine what it is?
I hope others more experienced & knowledgeable can give some direction & advise.
Praying you get some answers to help your little one. I know that has to be so scary for her, but also for you too.
Please keep up posted to let us know how she is doing.