I think Pinky McKay has something in her toddler tactics book about children knowing what no means and even shaking their head while doing exactly what they shouldn't be doing. DS does the same occasionally - it is an impulse that they haven't yet learned how to control.
I am reading this book atm and came back to this thread bc I just read that part!!
It says that although at age 1 babies might know what the word 'No' means their brains haven't developed the impulse control yet to actually be able to stop themselves. So that's why my DD will touch something she's not allowed to and look at me and shake her head. Not until they're closer to 2 yrs do they have the impulse control to be able to stop themselves. So keep trying to teach her but also baby-proof the dangerous things