M..
One of the things I learned quickly with napping and bed time is timing is everything with children. You must pay close attention to their early signs of tiredness in order to catch that window of opportunity. Because if she moves through her window of tiredness and goes into that "second wind", it will buy her another hour or two of alert time before she re-enters her tired state. The good ol' rush of adrenaline.
Watch for these signs of fatigue; your baby may demonstrate one or more of these:
* decreasing activity
* quieting down
* losing interest in people and toys
* rubbing eyes
* looking "glazed"
* fussing
* yawning
* laying down
* asking for a pacifier or bottle or to nurse
Naps should occur immediately when you see one or two of the above signs. It sounds like most of the days you are placing her down for a nap at the right time and the other two days, she has hit the second wind.
The recommended guidelines for a baby that takes one nap a day, is early afternoon.
My son is 17 months old and we use the same routine everyday. Eat lunch and then take a nap. It usually runs between 12:30 pm -1pm, some days it is earlier, some days it is later. I just watch for the signs and go to his crib immediately. If he does not go to sleep, I place a blanket on the floor, tell him to grab his pillow and blanket, and it is time for nappy with mommy. Then, I lay down, say night night, and close my eyes. He usually is asleep within 10 minutes...
Hope this helps....
The only thing that concerns me about your little one being in the crib for two hours at this stage of development is this might be a control issue. Let's see how long I can stay awake before mommy makes me take a nap. The crib is a wonderful cozy and safe place for the little ones, but two hours makes a red flag go off. Could be wrong on this one, but I would try the above and see if anything changes over the next week.
Good luck!