The woman, Mahlet, whose second name is not known, was speaking as part of a Young Black Leadership Summit at the White House.
She encouraged people to pray for the nation and fight for the "Godly principles" the country was founded on.
Mahlet, who talked about being adopted from Ethiopia at 11 years old, thanked God for giving the US "a great leader like Donald Trump".
She added in her prayer: "God protect us, protect our president as he's going through so much scrutiny. I believe you gave him to us and I believe he will accomplish so much more.
"The enemy tries to attack us every single say and discourage us every single day, but he has no room no more."
Mahalet was born in Ethiopia.— Benny (@bennyjohnson) October 5, 2019
Abandoned by her parents, she lived as an impoverished orphan.
Mahalet was adopted by a loving, Christian American family at 11.
This week @TPUSA brought her to the WH. She asked to pray for our President. He brought her onstage-then this happened: pic.twitter.com/kYoUT365Rq
Mahlet's prayer on Friday came as the Democratic Party began efforts to impeach Mr Trump.
They issued subpoenas to US defence secretary Mark Esper and acting White House budget director Russell Vought.
The House intelligence, oversight and foreign affairs committees are investigating Mr Trump's actions pressing Ukraine to investigate Democratic rival Joe Biden and his son potentially interfering in the 2020 election.
Mr Trump also withheld hundreds of millions of dollars in military assistance to Ukraine.
Democrats said the documents are needed to examine the sequence of events and the reasons behind the White House's decision to withhold aid appropriated by Congress to counter Russian aggression.
On Tuesday night the White House declared it will not co-operate with what it termed an "illegitimate" impeachment probe.
Lawyers for Mr Trump sent a letter to House leaders threatening them to cease co-operation with Capitol Hill on key oversight matters and accusing lawmakers of formulating their probe "in a manner that violates fundamental fairness and constitutionally mandated due process".
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