Boa Sandersonia is one of the three Gorgon sisters that rule over Amazon Lily. She and her sisters are called the Gorgon sisters for supposedly heroically slaying a monster called the Gorgon. She is the younger sister of Boa Hancock and the elder sister of Boa Marigold.

Appearance; Personality; Abilities and Powers; Devil Fruit; Trivia:
Appearance:
Sandersonia is a large woman who resembles a snake. Her large head is shaped like that of a snake's and her tongue is forked. Like the rest of the Kuja, she dresses in very revealing clothing. She is usually seen accompanied with the large panther, Bacura, at her side instead of a snake like the other Kuja. On her back, covered by her cape and her long green hair, is a mark of slavery branded on her by their previous Tenryuubito masters. It resembles a hoof mark and is a sign that means that she is "less than human" since she was a slave. Her sisters share this mark as well on their backs.
Due to this shameful mark's meaning, Sandersonia and her sisters made their fellow Kuja believe that on their backs were a set of eyes she and her sisters received as part of a curse for slaying the Gorgon. They told them that these eyes turned anyone who sees them into stone. If any of the Kuja found out the truth, Sandersonia and her sisters would be forced to leave the island.
Personality:
Sandersonia appears very fond of her sister Hancock as noted by the fact she laughed at her sister's "twisted" personality. While she appears to be living on the lie that her sisters and herself defeated a Gorgon to gain their curse, at the same time she hasn't actually told a lie herself unlike Hancock who is constantly lying. Sandersonia is the most emotional of the 3 sisters and highly emotional about their past, her crying had to be eased by her sister Marigold and drove her to collapse onto the floor.
In battle Sandersonia is a playful warrior who teases and torments her victims before she crushes them.
Abilities and Powers:
Ruling beside her sisters, Sandersonia has power over Amazon Lily and the rest of the Kuja women. Being a part of her sister's pirate crew, she is one of the elite Kuja warriors.
She possesses an ability similar to the Mantra of the Sky Island Priests. Using this, she is able to read an opponent's movements and avoid their attacks. The reaction of the Kuja warriors implies that this is a form of Haki. While she can do this, she being able to read an opponent's movement, although it is useless if said opponent is drastically faster than she is.
Devil Fruit:
While she was a slave, Sandersonia was fed the Hebi Hebi no Mi, Model: Anaconda as part of some sick form of entertainment for her former Tenryuubito masters. This Devil Fruit allows her to turn into an anaconda. While these powers are Zoan Devil Fruit based, the Kuja of the island have been made to believe that Sandersonia's and Marigold's ability to turn into snakes is part of the curse the sisters made up. In their transformed forms, the other Kuja state that Sandersonia and Marigold can do a battle formation called Saragi Dance.
Trivia:
Her name comes from the flower Sandersonia.
While Sandersonia and her sisters' title, the Gorgon Sisters, comes from supposedly slaying a monster with the same name, their concept is loosely based on the three actual mythological Gorgon sisters which includes the famous Medusa. Sandersonia is also able to convert her hair into snake-like, snake hair was another gorgon trait.
(Source: One Piece Wiki)