interpretation of a simple phrase

The display of dignity is pathetic because it arouses feelings of sadness in the poet....because of the awful circumstances in which the woman maintains her dignity.

The overseer is sneering to show contempt for the woman or for the slaves generally....it is interesting to wonder whether the woman's dignity forces him to see the fact of her humanity and courage and strength, and he sneers to try to shore up the convenient belief that the people he oversees are sub-human which he uses to protect himself from the horror of what he does?

A cane stands upright....the woman stands upright with dignity the poet sees as royal...or perhaps he is likening her to a cane that might be used by royalty (one thinks of a sceptre, I suppose?) Slaves were often used to work in fields of sugar cane.

I think the metaphor of the water pot growing from her head is a way of saying that the woman has retained the dignity and integrity of her roots in Africa....that she has refused to act submissively and has retained the essence of herself despite her awful situation.

Carrying a "water pot" is related to the upright posture.

Yes, but think it more than that.