My guess. The mistake she made is not that Barry was supposed to die but the baby was. Since it was being used as a conduit to Devoe's mind he imprinted his engrams on her. When she grows up she will become The Thinker mk2. Next season the team will travel forward in time to free young Jenna from the control of Devoe.
My reason for this guess is primarily because in that first shot of the baby she just stared directly into the camera with those huge dark eyes and they chose to linger on that shot.
Or....because it was a cute baby.
But I agree something will be up with that baby in the future.
And if all they had to do was get Ralph to that swirly orange thing - why didn't they just run into it right away like they did after the 17 fights with all the DeVoes?
Just to have their "Matrix" moment I guess.
And what happened to all the powers DeVoe had? Sure Ralph took control of the body back but it still has all the dark matter from the 11 other meta humans.
I wonder what Harry we get next season.