According to this Skanda Purana stoy Goddess Gayatri was actually a milkmaid who was married to Brahma when Saraswati took time to get ready for a Yagna that they were supposed to perform together:
"The priest returned, and thus addressed Brahmā: 'Savitri is engaged and will not come; but without a wife what advantage can be derived from these rites?' The god, incensed at the conduct of Savitri, thus spoke to Indra: 'Hasten, and, in obedience to my order, bring a wife from wherever you can find one.'
Indra proceeded accordingly; and as he passed hastily along, saw a milkmaid, young, beautiful, and of a smiling countenance, carrying a jar of butter. He seized her and brought her to the assembly, when Brahmā thus spoke: 'O gods and holy sages, if it seem good unto you I will espouse this Gāyatri, and she shall become the mother of the Vedas, and the cause of purity to these worlds!' Upon this Brahmā was united to Gāyatri, who was led into the bower of the bride, and there arrayed in silken garments, and adorned with the costliest ornaments.
In Chapter 9, Book 12 of Devi Bhagwat Puran she is extolled in absolutely glowing terms:
“O Devî Gâyatrî! Obeisance to Thee! Thou art the Great Vidyâ, the Mother of the Vedas, Higher than the Highest; Thou art Vyârhiti represented by the Mantra ‘Om Bhur Bhuvah Svah,’ O Mother! Thou art the state of equilibrium, i.e., the Turîya; Thou art of of the Form of Hrîm; Thou art Svâhâ and Svadhâ; Thou grantest the desires of the Bhaktas. Thou art the Witness of the three states, Jâgrat (waking), Svapna (dreaming) and Susupti (deep sleep). Thou art the Turîya and Sachchidânanda Brahmâ. O Devî! Thou resident in the Solar Orb and appearest as a ruddy girl in the morning, an youthful maiden at noon and a black old woman in the evening.
I want to know who this simple cowherdess could be who was turned into the 'Mother of Vedas' & if there are any stories in some other scriptures that talk about why she was qualified to be given that title? Also if she was just a regular human why is she shown with so many faces and arms with the weapons of the trinity?