"She is such an incredible player, an idol for me growing up and an inspiration for so many young boys and girls all over the world," Horan told reporters on the eve of the gold medal showdown at the Parc des Princes in Paris.
"Every time I face her I get so excited. We are pumped that she gets to see the field tomorrow."
Marta, 38, is appearing at her sixth Olympics and will return for the final after serving a two-match suspension for a red card picked up in Brazil's final group game.
That sending-off, for a reckless challenge on Spain's Olga Carmona, threatened to be Marta's final ever act at an Olympics.
However, having squeezed out of their group as a best third-placed team, Brazil shrugged off Marta's absence to claim an unexpected win over hosts France in the quarter-finals before stunning World Cup holders Spain in the semis.
"It is just a dream come true for us to be playing with Marta, to be able to get to the final and for her to be at her last Olympics with the chance to get the gold medal," said Angelina, the USA-born midfielder who wore the captain's armband in the 4-2 win against Spain in the last four.
Marta, a multiple winner of the FIFA world player of the year award, is hoping to bow out of the Olympics by avenging Brazil's defeats against the USA in the finals in 2004 and 2008, both games in which she played.
It remains to be seen if Saturday's game will turn out to be her last in international football entirely, or whether she could be tempted to keep going until the 2027 World Cup which Brazil will host.
"To witness what she has done on the pitch, for all of us who love the women's game she has been more than just a role model and an icon, she has been the best player over a long period of time," said USA coach Emma Hayes.
"What she has done for Brazil and for those women, you look at the generation coming through and the inspiration she has been to them. I am happy for her she gets the opportunity off the back of a two-game suspension."
