I agree with Mammo. The Klonopin really needs to reach steady state and remain there to prevent panic attacks.
Klonopin in normally not prescribed on an "as needed" basis. It's normally prescribed 1 to 3 times a day. It needs to be taken regularly at the same time(s) each day for best results. You need to discuss this with her prescribing doctor, I think not taking it regularly could cause some issues like she just experienced. I hope this helps and best wishes.
Klonopin PRN isn't always as effective as we would like. Perhaps it did not fully take away the anxiety and that was the feeling she was left with. If it continues to happen I would see the doc. Maybe the dosage is too small or she needs something faster acting PRN.
So this happened one time in 6 months? I think that would be just a fluke if its a continueing issue I suggest she see her doc.lily