I would like to know in detail about the incident where Ramakrishna prostrated before a prostitute and referred her as Maa Kali? Why and under what circumstances he referred her as Kali?
There are multiple occassions on which Sri Ramakrishna saw prostitute and instantly got a vision of Divine Mother.
Gospel / Volume 2 / The Master At The Houses Of Balaram Aand Girish:
One day I was riding in a carriage. I saw two prostitutes standing on a verandah. They appeared to me to be embodiments of the Divine Mother Herself. I saluted, them.
Gospel / Volume 2 / The Durga Puja Festival:
While meditating in the Kali temple I noticed Ramani, a prostitute. I said, 'Mother, I see that Thou art in that form too.' Therefore I say one must accept everything. One does not know when or how God will reveal Himself.
Gospel / Volume 1 / With The Devotees At Dakshineswar (I):
One day I saw a woman in blue standing near the bakul-tree. She was a prostitute. But she instantly kindled in me the vision of Sita. I forgot the woman. I saw that it was Sita herself on her way to meet Rama after her rescue from Ravana in Ceylon. For a long time I remained in samadhi, unconscious of the outer world.
After realizing God, one sees God everywhere and in all beings, this was the reason why Sri Ramakrishna saw Mahakali in prostitute as well.