Normal Nap Behavior?

DD used to be an excellent napper.  Most days I could count on 2 naps ranging between 1-2 hours and a third cat nap in the late afternoon.  However, since she turned 6 months, she rarely naps longer than 40 minutes.  This has resulted in 3, sometimes 4, naps per day.  I stay at home with her, so I watch for her tired cues before putting her down.  I have also tried letting her chat/fuss in her crib when she does wake up early, but rarely does she go back to sleep.  She's seems happy and rested most of the time, but recently there are days where she seems tired after only being awake for one hour.  Is this just normal or something she'll outgrow?  Should I even be concerned about it?

FYI, she just started sleeping better at night.  (Thank goodness!)  She falls asleep around 8:30 and gets up for the day usually between 7:30 and 8:00.  She wakes up once to nurse sometime between 2:00 and 5:00.