Some TMNT stuff really isn't for little kids.
Angel Bridge is an ally of Casey Jones and later the Turtles as well as crime fighting partner to Alopex. Like the version of Angel in the 2003 TV series, this Angel is a former member of the Purple Dragons gang (which she in the IDW comics had joined shortly after the accidental death of her mother). But unlike her parent incarnation, she appears to be older and more of a skilled fighter, and was the leader Hun took over from. At the time the Dragons were still a violent street gang, and Angel threatened to slip into a life of crime. One of her childhood friends Casey, whose father and her own were close friends, confronted her at approximately the same time her mother was lost, and brought her back to reason, an act for which Angel was sincerely grateful. Their conversion was also ultimately responsible for ensuring that the Dragons reorganized its leadership under a vigilante.
One day the Ninja Turtles were forced to look for a new home by Baxter Stockman, his M.O.U.S.E.R.S. and Old Hob, where they came upon April O'Neil in her father's old antique shop which was observed by Angel. Since the Dragons already had unpleasant encounters with other mutants from the Foot Clan, there was a battle between the Turtles and the Dragons until Casey joined them and was able to clear up the misunderstanding. Despite some reservations Angel eventually helped the Turtles, free their father Splinter from the clutches of The Shredder, and supported them from than on against the occasional machinations of the Foot Clan.
Finally, the leadership of the Purple Dragons was wrested from Angel by force, by a resurrected Hun. As a result the Dragons reverted to their former existence as a violent street gang. Then Angel disappeared from the passage and stood in the subsequent conflict against the Foot and the Dragons on the side of the Turtles and their friends.
In Teenage Mutant Ninja Turtles issue 34, When she visited the paranoid inventor Harold Lillja together with Donatello and April, Angel dons Harold Lillja's exo-suit in order to stop the rogue combat robot Metalhead. When Lillja asks her for her name again after she beats Metalhead she says she's "Nobody" and began to tackle the crime in the streets of the city. Finally, she met Alopex, who warned her of a plot against the turtles by Bebop and Rocksteady.
After helping the Turtles defeat Bebop and Rocksteady, she then teamed up with Alopex to fight crime. This became a habitual practice for the two, but Angel remained close to Casey and never hesitated to defend him when his father came too close, such as when Hun attacked the O'Neils' antique shop.
They also remained at the Turtles' disposal, such as when they helped them defend themselves from Baxter Stockman's flyborgs and M.O.U.S.E.R. robots. Angel was present but did not participate in the Gauntlet, where she witnessed her friends taking out the Foot's enemy mutants.
In the aftermath of the Foot's upheaval, Angel and Alopex also gathered valuable intelligence, with Alopex fighting one of the Street Phantoms while Angel filmed the encounter. She also assisted Donatello in testing the equipment that Harold Lillja had created to combat the Phantoms, but was forced to flee after an EMP blast disabled her exo-suit. She accompanied Splinter and the Turtles on the mission to rescue Harold from Darius Dun, where she fought his forces and was left to take care of Harold and his ex-wife Libby Meitner.
After the Turtles' departure from the Foot Clan, she remained close to them, and was a guest at the Turtles' Christmas party. While Harold Lillja had severed ties with Donatello, he remained in contact with Angel in order to keep her exo-suit in working order.
Shortly thereafter she and Raphael traveled to Alaska in order to bring back Alopex, who was cared for by her crime-fighting partner as she recovered from Kitsune's brainwashing. During a trip the two took to Northampton, they found themselves abducted by Toad Baron and forced to stay in the Den of Delights against their will. They managed to escape by starting fights and smashing objects within the Den, and Angel discovered that her armor had tracked their location.