Hiya!
Right now you're in the middle of the day sleep development period. 40-45 min naps are completely normal for this time. You'll have on and off days, but more off days than on for about 3 weeks. Eventually though, I promise, it will work itself out
My lo wasn't exactly up to 2 hours waking time until close to 5 months. However, because every lo is different, yours may be ready for it.
The most you can do during this time is get your DD as rested as possible. Keep pushing toward a 2 hour waking time. Don't sweat the short naps...they're gonna drive you crazy if you let them. The crankiness factor is par for the course during this time
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Nap length (if you can get a long nap) should be about 1.5 hours in the am, and 1.5-2 hours in the pm. If your DD gets about 10-12 hours at night, she'll take a shorter am nap automatically for the most part, assuming night sleep was restful. The am seems to be an extension of night sleep, sleep cycle wise.
Hope this answers all your concerns!
*HUGS*
Sonya =P