Declaring that her hips are "big" right in the first line makes us realize that the speaker is reclaiming the word "big." It's no longer an insult. It's an affirmation.
these hips are mighty hips. (11)
Notice how all of the descriptions in this poem begin with the phrase "these hips are"? Our speaker's completely sure of how her hips look and act. There's no "these hips might be" or "maybe my hips are." Nope, she's sure.
these hips are magic hips. (12)
If you weren't thinking that these hips seemed superhuman before, you probably are now!