Details are light, as they’re keeping the character’s name and even which episode she’ll appear in under wraps, but the CW has cast Vanessa Williams (the other one, not the singer).
On the show, Joe West hasn’t revealed much about what happened to Iris’ mother, though it’s been implied that she died some time back. Whether we’ll be seeing an alternate reality version, or whether Joe has simply been allowing people including their daughter to think that she died — or even whether she’s been allowing them both to think she’s dead — remains to be seen.
In the original comics, Iris’ parents are Ira and Nadine West — or rather, her adoptive parents are. Her birth parents Fran and Eric Russell sent her into the distant past to escape a devastating 30th-century world war. (They survived the war, and later reunited with their daughter.) She has two adoptive siblings, Rudolph (Wally’s father) and Charlotte. In the New 52, Iris’ father is William West, and her unnamed mother died when she was very young. In this version, she has two brothers: Rudy (still Wally’s father) and their younger brother Daniel, who would go on to find his own connection to the speed force.