The Flash will be adding another Justice League member from the Detroit days. This was a very different, trimmed down JL with Aquaman and Martian Manhunter as the only two holdovers from the previous teams. Maybe Zatanna and Elongated Man were a hold overs too. But, they added Steel, Vixen, Vibe, and of course Gypsy.
Cynthia Reynolds grew up in a normal suburban household, always going barefoot. After the birth of her brother, things began to change. Her parents argued constantly and Cynthia suffered some abuse. At the age of fourteen, her illusion abilities began to manifest and she chooses to run away, heading to Detroit.
She would use her illusion powers to protect herself on the streets, taking on the persona of Gypsy. She became something of a myth among the people on the street. Just by chance, the area she now called home was also the part of Detroit that Aquaman decided to start the Justice League again with a new roster. She finds having the JL in her backyard a challenge and tests herself by sneaking into their facility. Eventually she follows along with the team and helps out against Overmaster. This earns her an invite to join the team.
With the League she would improve on her abilities, becoming a better fighter and acrobat. She helps take on foes like Anton Allegro, Amazo and the Royal Flush Gang. She taps into other abilities including astral projection and precognition. She for saw the deaths of her teammates Steel and Vibe which ended up happen at the hands of Dr. Ivo. Gypsy escaped with the help of one of Ivo's androids and returned home. She left the Justice League.
This didn't turn out well for her as Desparo came after her, looking for revenge and murdering her parents. She is saved by Martian Manhunter and the rest of the JL. Gypsy and J'onn J'onzz would become close, forging an almost father / daughter relationship. She would work with Booster Gold for a while as part of the Conglomerate, but would eventually rejoin J'onn J'onzz as part of the Justice League Task Force wile it was together.
Gypsy would also spend time with the Bird of Prey and helping other heroes like Wonder Woman and Vixen. The more she uses her abilities, the more powerful she seems to become, not being able to use her illusions to shield not just herself, but a group of people.
She has two basic powers: illusion casting and telepathy. With the illusions she can use them to make herself or a small area invisible. She can also use her powers to create a manifestation of someones worst fear. Great for freaking people out. Telepathy wise she can astral project and get's flashes of the future. She is well-trained in hand-to-hand combat, acrobatics and firearms though she carries none on her.
She was created by Gerry Conway and Chuck Patton in Justice League of America Annual #2. This was also the first appearance of Vibe. In the television series, Gypsy is supposed to come in and help Vibe with his powers.
Update – It was pointed out in the comics that I skipped over her time in the New 52, which is true. Here she was a refugee from an alternate dimension that had been captured by Amanda Waller and held in a government facility. She is fleeing from Rupture, Vibe's brother who is servant of Mordeth… who is also this Gypsy's father. This all takes place in the Justice League of America's Vibe series that was written by Flash executive producer Andrew Kreisberg.