The South Africans scored eight tries in a strong all-round performance in front of a big crowd at Stade Makis in Antananarivo.
Louis Koen's team played with structure, kicked tactically well and put in a strong defensive performance, often turning defence into attack, and they were brilliant on the counter.
The Bok Women's pack also set the tone yet again with a commanding display, which allowed the backs to attack with space.
Zintle Mpupha scored first, in the fourth minute, off the back of a great maul. Ten minutes later Mabenge scored her first try from a turnover, and her second followed in the 24th minute from a massive South African scrum.
Libbie Janse van Rensburg converted twice to put the Bok Women ahead by 19-0, and three more tries in the final 10 minutes of the half - by Sizophila Solontsi, Chumisa Qawe and Mabenge - followed to make it 34-0 at the break, with a yellow card not helping the Kenyan cause.
Early second-half replacements, ill-discipline and unforced errors upset the South African rhythm a bit, but not too much as Mpupha scored her second try in the 49th minute after some great interplay between forwards and backs, despite Lusanda Dumke being shown a yellow card.
Mabenge and Unam Tose followed Dumke to the sin-bin, which allowed Kenya to apply some pressure courtesy of a string of penalties against the Bok Women, but the South African defence held firm.
Kenya finished the game strongly, but the South Africans' energy never waned and they kept their Eastern African opponents under pressure with very good defence. With time almost up on the clock, Mabenge added her fourth and Boks' eighth try.
Springbok Women 48 (34) - Tries: Zintle Mpupha (2), Nomawethu Mabenge (4), Sizophila Solontsi, Chumisa Qawe. Conversions: Libbie Janse van Rensburg (4).