What does Helen do to Annie moments after her arrival that causes commotion in the household in The Miracle Worker?
Well, you're right that it doesn't take long for Helen and Annie to begin butting heads! In fact, their very first encounter is a negative one. Of course, it involves something very significant and dear to Helen's heart: a doll. (Remember, previously Helen has insisted that her faceless doll be given eyes, so handling a doll with such beautiful features is truly a treat.)
Long story short, Annie won't allow Helen to hold/have the doll until Helen spells the word "d, o, l, l" into Annie's hand. There is a lot of kicking and screaming, but Helen finally does spell the word and gets the doll as a reward. However, Helen doesn't cradle the doll as Annie expects. Instead, here is what happens:
(She never finishes, because Helen swings the doll with a furious energy, it hits Annie squarely in the face, and she falls back with a cry of pain, her knuckles up to her mouth. Helen waits, tensed for further combat. When Annie lowers her knuckles she looks at blood on them; she works her lips, gets to her feet, finds the mirror, and bares her teeth at herwself. Now she is furious herself.)
You little wretch, no one's taught you any manners? I'lll--
(But rounding from the mirror she sees the door slam, Helen and the doll are on the outside, and Helen is turning the key in the lock. ...)
So there you go, ... Helen gets her revenge. Annie is literally whacked in the face (and even spits some teeth out in the movie!) and then locked in a room. As a result (and here is where the "commotion" you speak of comes in), Helen purposefully "loses" the key so that the entire family has to bring a ladder to the window in order to get Annie Sullivan out! A small commotion? I think so!
In reality, this encounter is less about the doll (or even the cake) but more about Annie starting her teaching method: the alphabet for the deaf that Annie so wants to help Helen learn. The actual commotion is actual quite vivid evidence that Helen is a smart (and a brave) little girl, ... who will one day thank God for her dear teacher, Annie Sullivan.