Hmm, it's a tough call at that age
My best advice is to experiment. Try keeping her up up to 15 mins more and see how she reacts. She sounds like she's right on the edge of needing to be pushed up at least 15 mins more of "A" time. It's common for lo's to take a good nap at the regular "A" time sometimes, and then sometimes not, waking up crying because they can't get back to sleep.
If being up 15 mins more is not the answer, try putting her down a little earlier...sometimes 5 or 10 mins makes all the difference for that fine line between the window and being overtired.
At that age I did quite a bit of experimentation. Mine got overtired easily too, so my best bet was to go with a little bit shorter "A" time as a rule.
Hope this helps a little!
*HUGS*
Sonya =P