Not even Lord Sauron could influence Shelob in her lair, Тояэcн Uиgol. As such, Sauron allowed Shelob to remain in her lair as she, despite her neutral affiliation, served as a defence gauntlet. She would be left untouched, untethered and unspoiled. She was left in torment of the war and did as she pleased, feasting upon those who would dare venture through Epнэl Duaтн. Her lair would serve as an impassable labyrinth in-which would be used to ensnare the enemies of Mordor. Shelob was the greatest offspring of Ungoliant, and paid no heed to the treacherous Orcs who were sent down to her in-order to prove their worth, who, with their efforts, came to no avail.
With an absence of activity with the great armies of Mordor being constructed, Shelob was bloated and had grown fat with the endless brooding of her feasts. She would sleep, eat, and sleep as there was no other purpose for her as of current; she served an idealistic lifestyle in the eyes of the Orcs, Uruk-hai and Lord Sauron himself for she protected the indirect, unorthodox route into Barad-dûr, and Mordor itself.
That's marvellous! I love saying that quote as it is true. Spartans describe themselves as slick and muscular; however, they cannot life one leg (hoof) off of its back. It is laughable.