one of my old hamsters used to do this too, randomly, in and out of the cage. my hypothesis is that my Syrian ham was experiencing some kind of neurological issue, like an absence seizure. they would last a couple of hours, during which time he would stare off into the distance not moving. if I picked him up, no reaction. the initial "seizure" would last up to ten mins and afterwards he'd be confused and dopy for the next few hours.
like others have said though, the most likely thing is that your ham is frightened or startled by something. try to work out if there's a pattern for when she does it. are there any stressors around the room - strong scents, lots of electrics (which can potentially buzz and stress animals), harsh lighting on her cage/tank, etc. are you handling her too roughly perhaps? many things to consider!!
I hope you can find an answer, but rest assured that it's probably nothing to worry about. she will probably grow out of it, and if not, as long as she's not in pain, it's all good.
