I'm not entirely sure which specific 'ruby witch' story you're referring to within 'Divinity: Original Sin'. There are many witches and magical elements in the game. If it's a custom or fan - made story, it would be different from the main game's official plot. In the official game, witches can often be found in areas related to dark magic or ancient secrets. They might be involved in battles, either as foes or as allies depending on the player's actions and choices.
The 'Divinity: Original Sin' series is known for its rich and complex stories. However, without more specific details about this 'ruby witch' in the story, it's a bit hard to give a detailed account. Generally, in 'Divinity: Original Sin', the game is filled with magic, quests, and a diverse range of characters. The witch could potentially be a part of a side - quest, a key character in a certain area's lore, or related to some magical items or spells.
In the 'Divinity: Original Sin' universe, a ruby witch could potentially have a very interesting backstory. If we consider the general themes of the game such as the struggle between good and evil, the search for power, and the discovery of ancient secrets, the ruby witch could be a central figure in a plotline that involves a powerful ruby - related magic. Maybe she is guarding a ruby that has the power to change the fate of the world, or she could be using the ruby's power for her own gain, either to fight against an oppressive force or to become an oppressor herself. There could also be a connection to other characters in the game, like a hero who has to either defeat her or convince her to use the ruby's power for the greater good.