Speaking in the afternoon at the Equality Forum at the University of the Arts, Castro said that she was "very proud" of the work she and others had done to promote LGBT equality and that she would push for gay marriage.
Castro, a sexologist and director of the Cuban National Center for Sex Education (CENESEX), has long been an activist for LGBT equality in Cuba. She has been credited with improving conditions for gay Cubans, who faced imprisonment as recently as the 1970s.
"We can make the best together," she said to a round of applause.
Malcolm Lazin, the Equality Forum's executive director, said Castro had made "real changes" to reduce oppression of gay men and women in Cuba.
As recently as Monday, Castro's visit to Philadelphia was in doubt. The State Department had initially denied her clearance to travel from New York, where she was visiting the United Nations.
That decision was reversed, and Castro arrived in Philadelphia on Friday and visited the Liberty Bell.
While Castro was well-received at Saturday's panel discussion, her visit drew some criticism, including from Rep. Ileana Ros-Lehtinen (R., Fla.). In a statement posted on her website Thursday, Ros-Lehtinen called the Obama administration "obtuse" for allowing Castro to travel to the conference.
"For a person like Mariela Castro to attend a conference on civil rights for lesbians, gays, bisexual and transgender people, and to receive an award, is shameful, pathetic and a ruse," the statement said. "The words equality and human rights don't exist in the vocabulary of the Castro tyranny."
Human Rights Watch, an independent advocacy organization, said in a 2013 report that Cuba "remains the only country in Latin America that represses virtually all forms of political dissent" and that in 2012, Raul Castro's government "continued to enforce political conformity using short-term detentions, beatings, public acts of repudiation, travel restrictions, and forced exile."
Speaking before the Equality Forum's dinner Saturday night, former Rep. Barney Frank (D., Mass.), who was also honored by the group, said that he applauded Mariela Castro for her work to expand LGBT civil rights, but that he would "differ with her very sharply" if she embraced the political repression of her father and uncle, whom he said were "among the great betrayers of liberalism and human rights."
"I'm glad that they're lessening the repression of gay and lesbian people, but no, I certainly don't think that people should say, 'OK, well, that's all you have to do,' " he said.
For the most part, Mariela Castro avoided political discussion Saturday. She veered from her gay-rights advocacy only when an audience member asked whether she expected relations between the United States and Cuba to change.
Responding in English for the first time that afternoon, Castro replied briefly.
"We have to change the world together," she said.
Contact Chris Palmer at 609-217-8305, firstname.lastname@example.org, or follow on Twitter, @cs_palmer.