Not a book review, since I haven’t read the whole book, but here is some interesting information about women’s ritual and Divine Mothers in lower Congo from: Phyllis Martin, Catholic Women of Congo-Brazzaville: Mothers and Sisters in Troubled Times. Indiana University Press, 2009.
Martin has turned up some important testimony about women’s traditional medicine and ceremony in western Congo. Nganga (plural banganga) is a very widespread name in Bantu languages, from the Atlantic to the Indian Ocean to the Cape, for a medicine person (of whatever sex), diviner, “spirit medium,” shaman. To induce conception and protect her through pregnancy and birth, a woman consulted a nganga skilled in these matters.
The nganga worked with minkisi (singular nkisi), ancestral beings whose power had been ritually embedded in a carved image. These ritualists were known as nganga nkisi. Some of them were guardians of minkisi in sacred groves.  German accounts around 1860-80 describe female nganga in shrines who dealt with female reproductive health and problems. Pechuël-Loesche tells of a Loango shrine for women and girls only, with armed protection guarding its perimeters: “Within it, the fetish* used by women from Lubu resided, healed and prophesied.” [See note below on “fetish” and cultural distortions.]
The statue showed a woman holding her breasts in her hands, in a style repeated in “innumerable small reproductions” used by women. “Mkissi [Nkisi] Mpemba was a gynecologist whose consulting days were associated with the waxing moon. In the second half of the month, at the time of the waning moon, it [sic] rested and gathered new strength.” The shrine was closed during the dark of the moon. [29-30]
Mpemba’s power was exceedingly great. Its fame reached to all territories. It had a large throng of women and girls who supposedly came to it even from the forest country [the Mayombe region] and even further in the interior…. Mpembe’s robe played the main role in the gynecological treatment in the fetish hut [sic], and besides that, a plank led down a slope through a hatch… Whatever else happened inside the fetish remains a mystery. For only girls and women who wanted a good husband, who wanted to be free of sufferings, who yearned for the joys of motherhood, who wished happily to survive their moment of giving birth, were allowed inside. [in Martin, 28]
Martin then lays out a shift that happened in the colonial era, when men began to see this shrine as a threat and destroyed it. There are several accounts of how this happened. One says that men from Loangili “had attacked the shrine and stolen, burned, or carried off nkisi Mpemba, or dropped it into a deep crevice during a moonless night. [Or, according to another local source]… “the men of Lubu are said to have committed the bad deed because the profitable activity and the increased power of the village women had become alarming to them.” This happened before 1870. Women were forced to abandon their ruined sanctuary but were rumored to continue holding ceremonies in secret.
Another women’s shrine, Mbinda of Buluango, rose to prominence with the destruction of Nkisi Mpembe sanctuary. The nkisi lived in a palm grove. Women who came for treatment abstained from men, hair care, tobacco, liquor and water. Mbinda too came under attack, the nkisi captured and thrown into the ocean. But her devotees rescued and reconsecrated her. Women flocked to these shrines in the Mayombe area and deep inland. 
The BaKongo are well known for the pfemba, their wooden sculptures of a seated mother with a child. Over 600
pfemba are known. They show the Mothers as icons of beauty and fruitfulness, tattooed, adorned with jewelry, and crowned with high coiffures or “prestige caps worn by authority figures in Kongo society.” They were anointed with red tukula paste, signifying “transformation and movement between different worlds, as in initiation and childbirth.” Some are inlaid with mirrors. Although it is common to see stereotypical descriptions about “fertility figures,” Mary Nooter Roberts writes that the pfemba “are one of the rare instances in African art where the female image is created specifically to assist with fertility.” [in Martin, 25]
Martin describes the wide popularity of small mother-child icons after the fall of the women’s shrines. Pfemba figures appear on tombs, doorposts and staffs of chiefs, household shrines, and musical instruments. “The French anthropologist Albert Doutreloux confirmed the high respect in which women were held, the genealogical knowledge that they guarded, the magical powers for which some were feared, and the kind of pressures they could exert in village discussions, including leadership roles when men were absent.” They spoke in public assemblies and had influence in lemba associations. However, the devastation of the slave trade, colonialism, and the rise of a merchant class undermined these traditions. [29-30]
This decline of female authority, and of old indigenous cultural patterns. is reflected in the loss of power of the Makunda. She was a leading royal official who was most often the sister or wife of the Maloango:
In the seventeenth century, she had great power, seeing to the interests of women, advising the ruler, and sometimes taking over the interests of the ruling clan during an interregnum. Her main function, however, was ‘to represent all mothers, who were the propagators of the tribe, who bore all the burden and worriment of procreation.’ Anyone could go to her court and ask for her justice, but she was particularly sought out by women and girls who had complaints against men. By the late nineteenth century, this power was gone…
Only a trace of it remained, as Pechuël-Loesche wrote, “practiced on a small scale by princesses with land, as far as their power is recognized at all.” Martin points out that women still had economic power through farming and trade, but their hard work did not bring wealth. She refers to matrilineality among the Yombe, but this too was now being leveraged for the political advancement of men. “Women were also centrally involved in the most powerful therapeutic association in lower Congo.” This was the lemba association. As Martin describes it, lemba was driven by traders, chiefs, and powerful men, (who were much concerned to suppress any witchcraft directed towards their wealth), but gradually lemba specialists moved more to pregnancy and childbirth. (I have to wonder if this was not the original focus suborned by the political developments referred to earlier.) [30,23]
*A note on “fetish”: this word has an objectionable history and connotation. I include the quote using it because it offers other valuable information. On nkisi, Martin refers to a comment that “no corresponding institution exists in European culture.” So the Portuguese word feitiçao (“sorcery” or “sorcery object”) was applied instead to these central African sacraments, carrying along with it all the cultural assumptions of European diabolism and witch persecutions. When you read about nails being driven into a “fetish” (the anglicized form), most often they are talking about a nkisi.
The minkisi came into play in slavery times, as a way to fight back against slaveholders (who feared them) in Brazil, Haiti, and Congo itself. [Some examples are given by one of Martin’s cited sources, Wyatt MacGaffey, Kongo political culture: the conceptual challenge of the particular. Indiana University Press, 2000. But much more documentation on this has been done by Africana scholars.]