When calling her womanly parts “diamonds,” the speaker is emphasizing her sexuality and pride in being a woman.
The context of the poem is how a woman can continue to bounce back after being beaten down. This can apply to a black woman or any woman. The poem is an inspirational one, in which a woman takes pride in being a woman and continuing to “rise” when beaten down.
Does my sexiness upset you?
Does it come as a surprise
That I dance like I've got diamonds
At the meeting of my thighs?
The key to interpreting this stanza is the first line. When the speaker asks, “Does my sexiness upset you?” she is talking about being held back by men, or even by other women. She is proud of who she is, and does not hide it. This makes some uncomfortable, or surpises them, including people who would objectify her. She sees value in being a woman.