https://www.gamespot.com/articles/why-shadow-of-wars-shelob-is-a-human-woman-and-not/1100-6453818/

As is to be expected from the sequel to Middle-earth: Shadow of Mordor, Shadow of War takes more than a few liberties with the Lord of the Rings canon. There's maybe no better example of that than Shelob, the giant, monstrous spider who is one of the main characters in Shadow of War, where she appears as a human woman. That's a form we never see her take in the books or movies, and it's understandably left some fans scratching their heads. But the alternative, according to developer Monolith, was to dramatically reduce her role.