Lipolelo Thabane was shot dead outside her home in the capital Maseru as her estranged husband was preparing to be sworn into office 48 hours later.
According to local reports, the Prime Minister and his first wife were negotiating their divorce before she was shot dead. Less than three months after her death, he married the suspected killer Maesaiah Thabane.
The shocking crime has gripped the tiny mountainous kingdom surrounded entirely by South Africa.
Maesaiah Thabane, 42, was remanded in custody after the murder charge was read to her on Wednesday. In addition, she was charged with the attempted murder of a second woman who was with the former first lady the night she was killed.
Reports said the 80-year-old Prime Minister announced last month he would respect the wishes of the ruling party and would resign from office at a date yet to be announced.
According to reports, the first lady became a prime suspect after she failed to appear for questioning in January in connection to Lipolelo Thabane’s killing.
She later turned herself in on Tuesday morning at a police station close to the border with South Africa.