There she visited a center now housing 121 children, including 33 aged five or under and four babies with their mothers.
The first lady's office revealed Tuesday that she would be making another visit to a detention facility as the administration continues to face questions over the status of the more than 2,000 children separated from their parents due to the president's "zero tolerance" policy.
But Mr Trump undercut the no-message message by tweeting that his wife was saying she really does not care about the "fake news" media.
It's the first lady's second trip to the border amid continued outrage over her husband's now-suspended policy of separating migrant children from their families when they cross the border illegally.
The first lady met with Border Patrol officials soon after landing at Davis-Monthan Air Force Base, where she said she was looking forward to touring the Border Patrol's facility in Tucson. Last week, her critics blasted her trip to visit immigrant children that the government had separated from their parents.
"If this is an issue of importance to the first lady, the field is vast for engagement and follow-up and her voice", she said.
For her second trip to the border to visit the border since the family separation crisis, Melania Trump has gone back to basics.
A staffer at the facility said the children had been there, on average, 48 days. The last time, "she wasn't able to visit a DHS facility, and she wants to learn from the people on the front lines at the border", Stephanie said.
Protesters spent Thursday morning outside a facility for detained children in Tucson that's operated by the non-profit Southwest Key.
In a related development, more than a dozen states sued the Trump administration on Tuesday over its separation of migrant children and parents at the US-Mexico border.
While most of the focus has been on President Trump over the course of the last three weeks, as Americans fight back against what they believe is an unjust policy of separating children from their parents along our southern border, Attorney General Jeff Sessions was actually the one who announced this policy. Federal officials were struggling to reunite children with their parents, some of whom were already deported.