yep - usually, topical creams, inhalers and nasal sprays containing corticosteroids aren't a big worry since they're more local, it's the oral stuff like Prednisone you really need to watch out for since it's more systemic.
either way, if she needs it, she needs it - just test more frequently and adjust her insulin accordingly.
I know I've had to be put on Prednisone a few times over the years and my BGs shot up to the 400s and would hardly come down for days. It stinks, but sometimes you have to weigh the risks vs. benefits.
I think she should be fine with the Nasonex