Deputies accused Kalaya Morton of being a "man" due to her gender expression, demonstrating how anti-trans laws can target cis women.
Chelsea Manning and Raquel Willis were among those arrested for peacefully protesting outside Speaker Mike Johnson's office.
The demonstration was in response to a recently adopted policy banning transgender people from facilities matching their gender identity.
The defendants were part of a trio that videotaped themselves harassing trans woman Alexa Negrón Luciano, who was later found shot to death.