18 month takes only one 30 min nap

18 month old toddler has been sleeping through the night since 3 month old. Has always had good night time sleep of at least 11 hours. Naps have always been short (40 min - 1hr each).

We've been on the 2-nap schedule for a while, and recently each nap has become even shorter (30 mins or sometimes 10 mins), though when we put her down she is sleepy.

That's when we decided to transition to 1 nap and do crib hour. Poor thing she gets sleepy at 10:30am but we try to keep her awake until noon.

However, after 7 days of training and lots of crying, nap is still short. Usually 30mins, 50 mins max. What do we do?

2 naps don't seem to work (which is why we transitioned in the first place). 1 nap doesn't seem to work either. Sigh....

Schedule:

6-6:30 am: wake up 12-1pm: crib hour (sleeps for 30 mins on average) 7pm: sleep