Mine's been similar (we're at 6.5 months here), but she's also teething. I think she wakes up initially from discomfort but has slept long enough at that point (4-5 a.m.) that she can't return to sleep right away. We calmly wait it out, like you.
As for the nap thing, DD's been leading the way to dropping a morning nap by just not really falling asleep during that first one. We do the routine, she gets sleepy, might close her eyes a bit, but then wakes right back up. We go about our day for another 1 - 1.5 hours, and then she, quite miraculously, usually will take a long nap at the time she would ordinarily have taken her second cat nap. Is there a way you could maybe do some quiet time with your LO, give her a bit of rest without her actually taking that first nap at the usual time?