Try not to worry too bad. Alot of the time if they show it early on like that they may get better with age. Like the last post said, as long as she can eat ok then its just something else you can love about her. Its a spider thing. They all have it. My bumblebee has a very mild head bob once in awhile when its feeding time and she gets excited. I held a male spider last year that I almost bought but I decided not to because he had the most sever case I had ever seen. I almost couldnt hold him at all. He flipped, flailed, twisted, corkscrewed, constantly. It was like he was trying to throw his self out of my hands. He couldnt keep his head or upper body upright at all. It was very bad. Yours sounds typical and not so bad so dont worry too much. It could be much worse.