napping questions

as of the last two weeks elenora has begun to play around during the majority of her morning and afternoon naps (usually either the first or the second, with a good nap for the other). Before this, she would sleep from 9-11 am and then from 1-3 pm (give or take a half hour) each day. There have been 3-4 days the past two weeks where she has played in her crib for an hour and a half in the afternoon, and not slept at all. When I get her up she is very pleasant and I just make sure to put her to bed by 6 pm. (Her bedtime is always between 6-6:30 pm and she sleeps until 6 am.) For a few mornings during the past two weeks she has played around in her crib and not fallen asleep for quite awhile. When she does fall asleep, I then have to wake her after 1/2 an hour to 45 minutes so that the rest of her schedule won't be thrown off for the day.

I am under the impression that this is too early for her to move to one nap a day. But her behavior seems to indicate otherwise, although there have been a few days in the last two weeks where she takes two naps just fine.

Should I press on with two naps a day and just let her play if she wants to play? Should I change the times of these two naps so they are shorter? Or should I begin the transition to one nap? What time is a good time for an afternoon nap if there is only one nap a day? What time should she go to bed at night, and will she start sleeping in past 6 am? I set my alarm for 6 am so that she has a regular wake up time (she's generally awake when I go in to get her), but if she starts sleeping later, how late should I let her sleep?