Pred reduction

I posted back in July - my daughter was having problems with her asthma being out of control. She came off Pred 4 weeks ago having gradually reduced and was good for 2 weeks before having an excacerbation - she then took a week long course which of course put her back on track and then 5 days later had another decline, she was then given 2 days of Pred which put her again on track and now she appears to be going downhill (within 2 days of finishing the Pred). It seems that the longer she takes the Pred for the longer it keeps her relatively symptom free after finishing the course. Would this seem normal - I thought once you finished taking the course then within a day or so the drug was out of your system? Any advice?