Ah - I see, I read it wrong
I'm not asthmatic but I'm trying to think if circular movement ones do make it more difficult to breathe in general. I tend to avoid them because of back problems. Scarey rides in general can be difficult to breathe on as you're screaming/laughing so much.
Was the ride in question the last ride you went on? If so, it could simply be that it tipped her over the edge as far as heart rate/breathlessness went.
Really just thinking aloud - I guess you'll probaby not get a difinitive answer. I would imagine that it's something she should just be aware of. At least now she knows it can cause a problem and can be prepared for it.