March Harriet, also known as Harriet Pratt, is a grifter and escort who wears a rabbit themed outfit. Eventually, she was enlisted by Tweedledum and Tweedledee to serve as the March Hare for their new Wonderland Gang.
History
Detective Comics
Her first appearance is in Detective Comics #841, where Batman investigates a growing new team of costumed crooks, "The Wonderland Gang". Led by the Mad Hatter and featuring Tweedledum and Tweedledee, they quickly amass high-class muscle from all over Gotham dressed as different Lewis Carroll characters, such as the Carpenter, the Walrus, the Lion, the Unicorn, and the March Hare. Finding the crimes somewhat amiss, Batman eventually tracks the gang down to the House of Mirrors at the Gotham Amusement Park. He finds Tetch, the Mad Hatter, spinning aimlessly on the Teacups ride. Sure enough, Tetch is victim of one of his own mind-controlling chips, which Batman removes. He then goes in and confronts the gangs real leaders, Tweedledum and Tweedledee. While Batman is battling the rest of the Wonderland gang, Tweedledum and Tweedledee both escape outside only to be subdued by the Mad Hatter, who beats them both unconscious with an oar. Batman calls Jim Gordon to tell him where to pick the gang up, and to make sure his men know to take it easy with Jervis Tetch, who really hadn't done anything wrong.
In Other Media
Batman: Arkham City
Although she isn't in the game, a costume similar to hers appears on dozens of mind-controlled henchmen of the Mad Hatter.
She does however briefly appear in the Batman: Arkham Unhinged comic "Vicki in Wonderland".