The brown arc Of the neck I cannot catch, (8-9)
In this early moment of the poem, the speaker has lost her grip—for reals. She cannot "catch" Ariel's neck. She has nothing to hold on to. She is completely powerless.
Hauls me through air— (15-16)
Again, we see the speaker in a position of powerlessness. She is "haul[ed]" through air by Ariel. She is the object, not the subject, in this stanza. She has no control, and thus, no power.
Godiva, I unpeel—Dead hands, dead stringencies.
And now I Foam to wheat, a glitter of seas. (20-23)
The speaker's transformation to a position of power happens in these lines. She "unpeel[s]" the things that are holding her back in life. She compares herself to the powerful sea, which overwhelms the wheat of the fields that she's passing on her wild ride. Note that her ascension to power is all in her head; nothing changes physically. It's all mental.