Being classified as a Black woman is very different in the US versus sub-Saharan Africa. This is a bit of a long post but hope it helps.
The US uses the "one drop rule." If you have some black ancestry, you can claim that you are black even if you do not have stereotypically African features. The US has certain racial categorizations such as quadroons (1 of 4 grandparents was African), octoroons (1 of 8 great-grandparents was African)
PBS explains one drop rule
Within African Americans there is the issue of colorism. Lighter skinned slaves, often progeny of the master, more often worked in the houses, had access to basic education to perform tasks and better food. Darker skinned slaves, worked in the fields with no access to literacy or good quality food. Compounding the literacy dividend head start over the generations has resulted in lighter skinned African Americans tending to have more wealth vs their darker skinned cohorts. This created an unfortunate association that lighter skin meant you were somehow "better". So, you have some individuals who are proud of being a lighter shade of Black or "passing" for White and are excited when their progeny have "blue blue blue eyes."
Africans have a far different understanding of race than Americans. In sub-Saharan Africa, you need two Black parents to be classified as Black. In Zimbabwe, where Sophie Chandauka is from, M, due to her mixed heritage would be classified as "Coloured" (0.5% of Zimbabwe’s population) and not “Black”, (98% of Zimbabwe’s population), so from a Zimbabwean point of view, M is not a fellow black woman to SC.
Apartheid was not only present in South Africa but was present in most of colonial Africa, from Kenya to Zimbabwe featuring racially segregated hospitals to be born, racially segregated graveyards to be laid to rest and racial stratification of life in between (schools, elevators, offices, prisons, etc.).
M would be classified as “Coloured” in Eastern & Southern Africa and “Half-caste” in West Africa. Coloured children were whisked from their families as soon as an authority spotted then and were raised by the state. The State then punished the parents with prison time. Trevor Noah in his book "Born a Crime" detailed how his mother's family hid him, and while outside his mother pretended to be his nanny so the South African state would not take him. Born a Crime by Trevor Noah
As you can imagine children raised in government orphanages did not have the best start to life as they were routinely neglected and ignored. To this day, social studies by race in former colonies such as Kenya or Zimbabwe show that the Coloured population is over-represented in crime, alcoholism, drug abuse, etc. Unfortunately, as a consequence, the Black African population looks down on the Coloured population as having no culture and no roots and views any marriage as bringing in problems to the family.