Although only about fifteen activists protested against the Progress Party politician's involvement, their shouts and boos could be heard throughout her speech, while their banners drew attention to the MP's controversial past statements on gay rights issues.
Horne took the criticism in good spirit.
"To make a speech when people are booing isn't the nicest thing you can do, but it went well," she told NRK.
In her speech, Horne expressed strong support for gay rights in Norway.
"Today, it is strange to think that homosexuality was ever prohibited," she said.
Gay activists' opposition to Horne centres on a tweet she once sent out about a children's book which included gay characters. "I wonder if it's okay that kindergartens are reading gay adventures to young children?" she tweeted.
However, since taking up the role of equality minister last October, Horne has consistently emphasized her support for gay rights.
"I will be the minister for gays, lesbians, transgender and heterosexual people," she said on appointment. "People should be allowed to judge me when they have got to know me."
As he called her up to open the event, Nils-Erik Flatø, the Norwegian comedian hosting the event, called for the crowd to forgive her past utterances.
"Who here has not posted something on Twitter that they regretted?" he said.
Line Halvorsrud, who leads Norway's Queer Youth organisation, agreed that it was right for Horne to open the festival.
"It's a natural job for the minister of equality and inclusion," she said. "What's more, the debate that has taken place because she was here is an important one: that we have a responsibility to stand up for the rights of all minorities."
Earlier this month, Horne's presence at a feminist festival in Malmö, Sweden, led to the organizers being heavily criticized.