|Devi has no caste. She therefore does not discriminate.|
As we all know, East and Northeast India has been hub of Tantric Shaktism ever since time immemorial and the rules of the worship of Devi primarily comes from Tantras.
Unlike male-dominant cults like Vaishnavism, where women are dependent upon their fathers, sons or husbands, Shaktism treats men and women alike and considers women as manifestation of the Divine Feminine:
"vidyā: samastāstava devī bhedā: striya: samastā: sakalā jagatsu | tvayēkayā pūritamambayētat kāte stuti: stavyaparāparokti: ||" (Devi Mahatmyah 11:6)
Oh Devī! The eighteen doctrines including Vedas arth thine parts. All women, endowed with thine sixty-four Kalās arth thine forms. Thou alone pervadest the universe from inside and outside as the birth-giver. The literal and esoteric description of the praiseworthy is called eulogy. When thou arth the form of all descriptions, then who arth competent of singing thy eulogy?
Unlike male dominant cults, Shaktism is all-inclusive and acknowledges the Divine even in the so-called 'backward' classes. That is why Shakta Tantras identify nine classes of women known as 'Kulanganas' or 'Navakanyas' as the Divine. Women of these nine classes are revered and can become Stri Guru (female Gurus) in Shaktism.
"națī kapālikā veśyā rajakī nāpitāńganā | brāhmaņī śudrakańyā ca tathā gopālakańyakā || mālākārasya kańyā ca nava kańyā prakīrtitā ||"(Guptasadhana Tantra 1:12)
Națī (dancer/actress), Kapālikā (skull-bearing Tantric), Veśyā (prostitute), Rajakī (laundry girl), Nāpita (barber), Brahmāņī (Brahmin), Śudra, Gopāla (milkmaid) and Mālākāra (gardener); women of these kinds are known as Navakańyās.
Coming to the question, the soil from the courtyard of the nine Kulanganas, including the prostitute, is collected to mould the image of Devi to honour them. Those who worship metal or stone images too should collect the soil and spread it at the base of Ghatam/Kalasham. Devi Puja is not complete if these nine women are not honoured either by worshiping their daughters in Kumari Puja or by making donations to them and feeding them.
Apart from this, the soil of seven Holy rivers (Ganga, Yamuna, Godavari, Brahmaputra, Narmada, Indus & Kaveri), soil from 51 Shaktipithas and soil from five animals (from elephant's tusk, lion/tiger's claw, wild boar's tusk, buffalo's horn and cow's hoof) are also mixed for making Devi's idol.
These days people know only of the prostitute's courtyard's soil since it was popularised by the Bollywood movie Devdas. But in reality, soil of these many kinds are needed. That is why Durga Puja is called Mahapuja, because it is difficult, costly and Devi is to be worshiped thrice in a day for five continuous days. That is why Durga
Puja is an annual affair.