Many lo's can't do a full A time after a short nap hun. Mine can, but that's a different story to BT! There's no way at all she'd do the same length of A to BT.
She's 8mo isn't she? I see that from one of your previous posts. At 8mo we were doing 4hrs, 3.5hrs then 2.5hrs.
How about you reduce that last A to 2hrs 45mins max and stick with it for a week. There may be a bit of separation anxiety at play too as this is the prime time for it.