In the season 6 finale of The Flash, Eva killed Carver, defeated Barry, and framed Sue Dearbon for Carver’s murder. Besides, Barry never found Iris, who mysteriously disappeared in a post-credits scene.
The Flash showrunner Eric Wallace has already confirmed that Iris’s situation will have “epic consequences” for the couple in the future. One of those “consequences” may be that Iris blames Barry for her situation.
Iris previously defended Barry for taking too long to save her, but if what’s happening to her brain makes her irrational, that opinion may change. Once Iris returns, The Flash could start a new delicate story with Iris.
If Eva’s mind was corrupted by the Mirrorverse, which seems possible, Iris could go down the same path having devastating mental lapses, either immediately or later in The Flash.
If The Flash season 7 were to move in this direction, Iris could spiral until she finally betrays Team Flash, feeling like they already betrayed her. Iris may not have any power, but her proximity to Barry would make her a threat.
Iris could even line up with The Flash’s next main villain for revenge. To solve this problem, Barry and his friends would have to find a way to reverse the damage done to Iris’s mind.