The Republican leader has been vocal about his opposition to mail-in ballots, often claiming without evidence that the process will be rigged against him.
Her plans to hit the trail with her husband last week were thwarted due to a "lingering cough" from her battle with the coronavirus, which struck the first couple and son Barron.
The United States remains the nation hit the worst by the pandemic, with the world's highest caseload and death toll, accounting for nearly 20 per cent of the global deaths.
Nearly 75 million mail-in ballots have been sent or requested so far this year, more than double the 33 million in 2016, according to the US Elections Project of the University of Florida on Monday.
As Trump prepared to leave the White House for the first time since returning on October 5 after three nights at Walter Reed Medical Center, he fired off a series of tweets.