In a description of her job that US vice presidents could have given, she said: "Now I get to be the tiebreaker if the House and Senate can't agree. And I have meetings with the president. That's all that I know that I do."
Her father, Albert Morales, said Martha waged a serious campaign to win, and he routinely posted campaign updates on his Facebook page. He revealed the results of the contest there, too.
Democratic political activist Bryan Weaver said a number of Albert Morales' friends saw his Facebook posts, got caught up in the election and were upset when Martha lost. "A friend of mine who runs a bar on U Street (in Washington, D.C.) welled up with tears," he said.
Someone who knows Clinton saw the posts and mentioned it to her, and she decided to write to the youngster. Her spokesman, Nick Merrill, confirmed that the letter is authentic.
"My mum was just picking me up from school, and she pulled the letter out of her purse," Martha said. "I opened it up, and it was a letter from Hillary Clinton. I was very surprised."
Albert Morales said: "My wife texted me a copy and said Martha was just very happy and excited and surprised that Hillary would take the time to write to her."
The 8-year-old, who is looking forward to turning 9 next week, is now working on a thank-you note.