"She" was a Maia, and evil, but Ungoliant served only herself. In an epic duel with Morgoth, over possession of the Silmarils, she nearly overcame him in Lammoth; and Morgoth was only saved by the coming of his balrogs from Angband, who issued forth at his titanic cry of alarm. Ungoliant went and dwelt in the north of Beleriand, beneath Ered Gorgoroth; "and that dark valley...was after called Nan Dungortheb, the Valley of Dreadful Death, because of the horror that she bred there. For other foul creatures of spider form had dwelt there since the days of the delving of Angband, and she mated with them, and devoured them; and even after Ungoliant herself departed, and went whither she would into the forgotten south of the world, her offspring abode there and wove their hideous webs. Of the fate of Ungoliant no tale tells. Yet some have said that she ended long ago, when in her uttermost famine she devoured herself at last." -- Sil page 81.

Shelob was the greatest of Ungoliant's children, somehow surviving the destruction of Beleriand at the ending of the First Age; and her offspring inhabited Mirkwood and the Ephel Duath. Her fate is unrecorded; but it can be surmised that she either died of her wounds, or perhaps starvation following the fall of Sauron, when she could no longer hunt - being partially blinded and lacking enough fresh meat.