I'd perhaps try pushing the morning A a little, I think.
I really wouldn't be tempted to start limiting the amount of day time sleep when on one nap, or stay on 2 naps for mush longer. There is a very fine line between coping and getting OT.
Most likely it is a period of adjustment really - and perhaps see if cutting that final A helps at all.
Are you still on 4.5hrs? Or is it 5 hrs as she is chatting herself to sleep?