Jenna is the Step Sister.
Glad they mentioned Kara, but still should have gotten her.
https://www.bleedingcool.com/2018/05/23/flash-season-4-finale-recap/
''We end at Joe’s house with everyone meeting Jenna Marie West and a surprise appearance of Wally West (Keiynan Lonsdale) to see his baby sister. Iris tells Barry that they’re next to have a kid, and you can see fear in his eyes. Ironically there is a knock on the door and we see that it’s the mysterious girl (Jessica Parker Kennedy), whom we’ve seen on and off all year. She just walks in and everyone recognizes her from when they saw her before. And Iris wants to know how she has her coat. The girl says Iris gave it to her and introduces herself as Nora West-Allen, Iris and Barry’s daughter from the future — and that she’s made a big mistake.''
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