Overlooked solution:

One strategy I'm surprised at least Barry didn't think of if not the girls:

First nuke JS's device so that she can no longer remember different timelines. Barry's laser could probably do that. Next, go back to the 90's one last time and exit the garage, then put some distance between them and her before jumping back so that she doesn't find their tachyons before they dissipate.

They got all the information they needed to get this idea before they had Barry take away their power.

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I'd've gotten away with it, too, if it weren't for you meddling kids.