She could be just sleeping.
I know that my little guy definitely has a pattern, and there is no waking him up when he is sleeping....he is aways active in the morning when I wake up...then he sleeps until about 1-2 in the afternoon..then kicks for a good hour....then nothing until dinner time....and then again crazy kicks from 9pm - 11pm.

They say that if all movement has stopped over 24 hours to call your doctor. But if you notice that she is moving at regular patterns, then I would say you are fine. Some of my friends didn't feel a lot of kicking at all...everyone is different. But if a baby goes from being very active to not active at all....mention it to your Dr.