Originally stillborn due to Zoom attacking her mother, Linda Park-West, Wally West travelled back in time while fighting Zoom and pushed him into his own blast, causing what the doctor's called "Spontaneous pregnancy" in the current timeline and reviving Iris and her brother Jai, being born happy and healthy. Iris is named after her great-Aunt, Iris Allen West
Shortly after, during the Infinite Crisis, Wally West was sucked into the speed force while fighting Superboy-Prime. Returning home to say goodbye to Linda, she grabbed hold of him while holding Iris and Jai and all four West's were sucked into the speed force. However, thanks to a key Linda was holding from the planet Savoth, the four of them actually ended up traveling to the planet Savoth, where the family was able to stay. The speed force had altered the children's genetic make-up though, and shortly after arriving on Savoth they began to age rapidly, eventually stabilizing when Iris was roughly 10 physically and Jai was 8 physically. The kids also developed powers, with Iris having the ability to vibrate her molecules through solid objects and Jai having the ability to accelerate the growth of his muscle tissue.
Back to Earth
During the events of the Lightning Saga, the Legion of Super-Heroes used their lightning rods to bring back the essence of Lightning Lad, however as a side effect of their actions, Wally, Linda, Iris and Jai were pulled back to Earth. Around this time, the kids developed powers, with Jai having the ability to accelerate the growth of his muscle tissue and Iris having the ability to vibrate her molecules through solid objects. She and Jai then started working with their dad to be super-heroes, and following a Ferry Rescue caught the attention of the media.
During the events of Flash: Rebirth, Iris discovers that she and her brother are sharing their connection to the speed force which caused their abnormal abilities. She decides to end Jai's suffering by giving up her connection but inadvertently obtains the full connection to the speed force, regulating her powers. She then joins the rest of the Flash family in battle against Professor Zoom as the new Impulse, a mantle she takes on much to the surprise of her father and Bart.
Road to Flashpoint
Iris and the rest of the Flash Family are at a picnic, but Barry never shows up.
In the alternate world of Earth-22, Iris West is the daughter of Wally West and Angela Margolin, rather than Linda Park. In this version, Iris has grown up to be the fourth Flash, although she is sometimes referred to as Kid Flash. Her older brother Barry is too lazy to take the mantle. In this world, Wally has all but ceased normal human activity, emanating from the Speed Force as a blurry Flash. Iris is quite bitter that she does not have a normal family life. She becomes a super heroine, part of a less than heroic new generation of superheroes.
During the events of Kingdom Come, she joins her fellow Titans children in Batman's Silent Cavalry, a new form of the Outsiders. She assists Batman in stopping Lex Luthor's Human Defense Squad when they take on Luthor and his cronies. Captain Marvel gets away, however, sparking a riot at the Superhuman gulag. In the ensuing chaos, Iris fights against the escaping convicts. When her father is wounded in the chaos of battle, she saves his life by depositing him inside of a protective bubble made by her friend Jade. She presumably is able to survive due to her super speed.
Later, when a madman named Gog attempts alter the past, Rip Hunter recruits Iris, along with Ibn al Xu'ffasch, Nightstar and Offspring. Ultimately, Hypertime is discovered, rendering this unnecessary.
Iris once again travels to the main universe when Donna Troy's existence is put in danger. This time, she travels with Nightstar, Donna's son Darkstar, the Red Hood and Tula, the Aquagirl of her timeline.