she may know what no means, that doesnt mean she can figure out for herself what to do instead... or how to react to a no answer.
the biggest asset you can have with a child is distraction. just give her something else to do. that way you are teaching her "no you cant do that but you can do this"...
kids under age 8 do not have inner speech. what this means is that when told something, when doing something, when experiencing something, they cant stop and say something in their head to themselves to solve their problem or whatever you know? its just not possible. :D
anyway, learn all you can about child development.
oh and one minor warning, you will be unpleasantly surprised when that tapping of her hand to stop her from doing something teaches her to do the same to you when you do something she doesnt like. ive found that its more appropriate and it works BETTER to actually just divert my son's attention than resort to something that hurts. some kids dont even react to a spanking. they just ignore it.
you do your best to keep the things out of reach that your child shouldnt have. half the battle is prevention! your child cant get into something that isnt within reach.