Well, simply put she appeared to act as a mindless or very dull individual. There is no sound, but in viewing the body language, she acts very much unaware of the danger presented by a man, who is masked, has a gun, and is demanding money (a very clear and distinguishable threat, for pretty much anyone normal). The possibility that he may decide to shoot over the counter, the very counter where her daughter is sitting, doesn't seem to cross her mind until shots were fired, then she jolts back as if awoken from some stupor or dream and mouths what seems to be "OMG!".
At no time during the moments prior to the shooting did she make any attempt to pull her child off the counter (out of the potential harm's way) or at least put as much distance between the girl and the criminal as she could. The most she did was scoot a couple of inches to her right and stare at the clerks pull out the money, as if the criminal was just another customer, that happened to be in a rush.
I apologize if you find the words I used as abusive, but I feel that they are merely descriptive of the behavior shown in the video.