Wendy-Lee, sorry to hear about all the problems your daughter has been having, and hope she is soon back to full health.
Do you think the high prolonged doses of pred, which were obviously strong could have dampened her immunity system at all? When my son was very young, (SWCAH) he had infection after infection (various types) for months on end and eventually he was given Gamma globulin injections which really improved things.
It might be nothing to do with your daughter's CAH of course, as many children do tend to go through these periods in their life but I can understand your worry. Hopefully Laura can shed some light on the rash, it is odd that it happens in summer but you must have been through all this I am sure.
Has your daughter seen a dermatologist for this at all? Just wondering if not, might be an idea the next time she gets the rash, (lets hope she doesn't), you take some photos, and ask for this speciality for their opinion as well. Good luck, please let us know how she gets on.
Hope she has a happy birthday (and you too Laura) and hope that you feel better soon too.