The Flash movie was originally supposed to be released in early 2018, but following the departure of two directors, the project went through a revamp. Now instead of being a traditional standalone story for the Scarlet Speedster, it's been changed to Flashpoint, based on the 2011 comic book storyline of the same name that led to the New 52 reboot. If you're familiar with that event, then you know that it's peppered with alternate versions of DC Comics heroes and villains, including some of Flash's Justice League teammates. It looks like the cinematic Flashpoint will remain faithful to that element of the story, as Wonder Woman will reportedly appear in the movie.
Gal Gadot has had a big summer thanks to Wonder Woman's critical and commercial success, and she'll be back in November for Justice League. Following that, Wonder Woman 2 will be released in late 2019, and according to Forbes, Gadot will reprise Diana of Themyscira for Flashpoint, which is aiming for a 2020 release. It sounds like she'll be giving Batman a run for his money for most DC Extended Universe appearances, though if this report is true, you can guarantee that she won't be the last Justice Leaguer to be included in Flashpoint.
For those not familiar with the story, Flashpoint unfolded when Barry Allen traveled back in time to prevent Eobard Thawne, a.k.a. Reverse-Flash/Professor Zoom, from killing his mother, Nora Allen. Barry was successful, but stopping the murder resulted in the main DC timeline being drastically changed for the worse. In this alternate timeline, Wonder Woman was waging war against Atlantis, led by Aquaman, her former lover. After Themyscira was destroyed, Diana and her Amazon forces conquered United Kingdom and turned it into New Themyscira.
The Flashpoint movie will mark the third adaptation of the storyline, the previous two being the animated movie Justice League: The Flashpoint Paradox and the first episode of The Flash Season 3, although the latter explored the consequences of Barry's temporal meddling for the rest of the season. If Wonder Woman does indeed appear in the Flashpoint movie, it's likely that Jason Momoa will also appear as Aquaman so the Amazon-Atlantean War can be properly realized. Let's also not forget Ray Fisher and Henry Cavill potentially reprising Cyborg and Superman, respectively, as the former is the U.S.'s top superhero and the latter has been imprisoned by the U.S. government his whole life. As for Batman, he died in this timeline, and Thomas Wayne (played by Jeffrey Dean Morgan in the DCEU) took on the mantle instead, but there could still be room to fit in Barry Allen visiting the Caped Crusader after the timeline has been restored to deliver a special gift.