It sounds like it could be night terrors - with only 1.5 hours nap and 5.5hrs between end of nap and bedtime, lo is probably overtired - and that just makes the transition between sleep cycles difficult. (I am sure you are aware - night terrors are nothing to do with dreaming etc, just transitional crying and thrashing around and going almost immediately back to sleep often wthout intervention, I just put a hand on H's back).
It may be worth either trying to make nap a little later until she lengthens it out, or bringing bedtime forward a bit. Ideally I would leave no longer than 5 hours from end of nap to sleep, and whilst naps are on the shortish side, I would err on the side of caution and go for 4 - 4.5 hours.
I often find with H, that he will settle v quickly when he is very tired - and then I know the chances are he will wake. he wakes at the end of the deep sleep phase approx 3 hours (or 3 cycles) after going down. So it seems to be they individually have their sticking points when overtired!
HTH
justine