How long is her current A time? Did you take a look at the link that lolsy shared near the top of this thread?
From what I have learnt, if they wake up either happy, or seem frustrated it's UT
if they wake up really grumpy and continue to be in a bad mood it's OT
It sounds like you may be right about UT for morning nap and OT for afternoon nap. I think if you get a short nap you need to decrease the A time before the next nap because otherwise they will just be too tired.
It's all so confusing!!