I'm at the same stage as you. 19.5 month old DS... waking up at 5:30, and naps are only 1.25-1.5 hours
He's also teething, cutting canines, so I'm attributing it to that. It's been three weeks of EWings now, but these teeth take forever to cut! Have you tried meds? Doesn't work for us, but some people have success even doing it a few hours before they wake up in the morning if you think she's waking up due to pain.