I took her to the doctor, who ruled out teething, an ear infection, or any other obvious cause of her frequent nightwaking. The doctor confirmed what I feared – she had grown so dependent on nursing to sleep that she couldn’t get back to sleep on her own.
I’d been working really hard over the past two months to get her to go down sleepy but awake. It seemed like we had made some progress, but when she failed to fall asleep after a few minutes of crying I usually went in and nursed her again until she fell asleep. That was only reinforcing the problem.