Engels suffered gashes to her forehead and head and opened a case of assault with intent to cause grievous bodily harm at the Sandton police station on Monday.
Two women who were in the hotel room with Engels described the assault.
"We were chilling in the room. Next thing this lady pushes into the room and started hitting us," said one woman who asked not to be named.
The second woman said: "It [the assault] lasted like half an hour. They basically held us hostage."
The two women decided not to lay charges, but were supporting Engels.
Police spokesman Brigadier Vishnu Naidoo said on Tuesday that Mugabe and her legal team were negotiating with the police before handing herself over.
"It was supposed to happen today [Tuesday]. It didn't materialise yet," he said at about 3.30pm.
- Additional reporting Nhlalo Ndaba