She may not be an Afrikaaner, but getting schooled in South Africa during that period would be a tacit acknowledgement that she did indeed support Apartheid.
Not all whites in South Africa supported apartheid, and one or two of the universities actively opposed the system. Alan Paton, a white South African, made the outside world aware of the racial situation in South Africa in his Cry, the Beloved Country (published before fully-developed apartheid was imposed in 1948)...he was of British descent, not an Afrikaner.
The Afrikaners are mostly of Dutch descent, with some French Huguenot and German mixed in, and can trace their families back to the 17th century, as long ago as the First Families of Virginia can trace their presence in America. It was the Afrikaners, not all of the whites, who were the strongest supporters of apartheid. The Portuguese have been in Mozambique and Angola even longer, but I don't think Teresa's family was of long-time African residence.