Aged 52, the first lady has dropped heavy hints that she aspires to the presidential palace and has publicly called on her husband to name a successor.
She has been increasingly active in public life in recent months and now leads the Zanu-PF women’s wing.
VP Mnangagwa, 74, was appointed to the post in 2014 and is seen by some foreign diplomats as the figure most likely to reform Zimbabwe’s fractious politics and moribund economy if elevated.
Mr Mugabe has already been named by Zanu-PF as its presidential candidate for polls due in 2018.
The president, who often travels abroad for medical treatment, has repeatedly condemned factionalism within his own party in thinly veiled rebukes to Mnangagwa and his wife’s public posturing.
President Mugabe said the party congress, held every five years, was mandated with the responsibility of choosing his successor.
The next Zanu-PF congress is due in 2019. He said that as a trained lawyer, he can not afford to violate party rules.
The Zimbabwean First Lady has gained political influence in recent years and currently chairs Zanu-PF’s women’s wing.
This has led some to speculate that she may harbour ambitions for the presidency.