I am glad you are having it checked out, but it's probably nothing. My son was about 2 when he started watching TV out of the corner of his eye. He would turn his head completely to one side and look at the TV from one corner only. Sometimes he would switch to the other side. It was always absent-mindedly - I would ask him why he was doing it and he would not be able to say why. He wasnt aware he was doing anything different. I was positive he had some problem with his vision or balance or something - it was truly odd to watch and I was a bit freaked out. In the end (after fun neurological and vision tests), the dr said it was a "tick". Basically he was just exploring - things looked a little different when you look at the TV like that, and it was interesting to him. He told me he would grow out of it - and he did (within a year).
My advice, though, is more on a different angle... You know how when you have a pain that bothers you enough to go to the dr but it doesnt hurt when you get there? So you cant describe exactly where it hurts or how it feels? Really annoying!!! I knew my son only did this while watching tv, and it wasnt 100% of the time... so I was worried about how to describe it. I didnt want my inability to translate it to the doctor to prevent him finding out something wrong. So I video'd him while he was doing it - including me asking him questions about it at that time (why are you turning your head? Can you see the tv? do you need to move closer? does it hurt?) and took that with me and let the doctor watch it. That was probably the best idea I have ever had! Even the doctor was thrilled - it gave him the comfort of knowing that his judgment was based on seeing it for himself, not on a secondhand account of a hysterical mom :)
It sounds like that might be a good for you as well - during the next month, take some video of her doing it. Take it several times (edit it so the doctor only has to watch the important parts) - you never know, you might notice a pattern yourself when you watch it objectively - such as its always when the lights are very bright, or only when you are cooking (smells, etc). And it will show the doctor exactly what your concern is. Talk to her during the videos so he can gage if she is interacting (i.e. if is some type of seizure, it would be important to note if she is responsive to your voice, etc).
I wouldnt be too worried, kids do some really odd "ticks" (I read up after that happened, and we definitely got one of the "minor" ones :). Spending the next month on a mission to document it thoroughly (time of day, circumstances, surrounding, most recent meal/nap, etc) will help you and your doctor if there is a trend, and keep you preoccupied during the next month so you dont worry as much. And if it turns out to be nothing, you will have the peace of mind of knowing your doctor was fully informed of everything he needed to know in order to make that decision.
Good luck to you! Let us know what happens!