Reports on Thursday said the incident took place on Wednesday.
According to Club of Mozambique, police confirmed the shooting, adding that she died on her way to the hospital.
Muiuane had since been arrested and remained in police custody.
A BBC report said that Valentina was "shot several times".
The 36-year old was listed as the seventh most powerful woman in Africa by Forbes magazine in 2013 and occupied prominent positions in the telecommunications and banking sectors. She also headed her family investment holding company, Focus 21, Gestão e Desenvolvimento, Lda.
She leaves behind a daughter.