They're all different. Natty didn't drop her morning sleep until about 14-15 months. But she ditched her day sleeps altogether at around 2.5 years, earlier than her little mates (some of whom still sleep for a couple of hours in the day. Ooooh, how serene... ).
I'd keep plugging away - all will be revealed. She will either go back to how she was or she will drop it. I found with Natty that she just sorted herself out, really. Hopefully you find that if she does drop it she will have one lovely big day sleep (which I actually found easier! You can plan your day better and get quite a lot done). GL.