Barbara Gordon, also known as Batgirl, has been paralyzed from the waist down in many Batman stories. During that time, she served as Batman's master hacker, providing the Caped Crusader with information under the moniker of "Oracle." It's clear from the trailers for Gotham Knights, however, that in this continuity, Barbara has regained her ability to walk.
There are a few different possible explanations for this, but considering the fact that Bruce Wayne is dead in the Gotham Knights timeline, it wouldn't make sense for the game to take place before Barbara was paralyzed. Instead, it's likely to pull from other continuities in order to explain her recovery.
The Origins Of Oracle
Barbara Gordon was originally paralyzed in Alan Moore's The Killing Joke. While the story was never originally intended to be a canonical entry to the main Batman stories, other Batman writers decided to include Barbara's paralysis in their versions of the character as well.
In The Killing Joke, Batman travels to Arkham Asylum in the hopes of finally ending the destructive cycle of violence between himself and the Joker. However, upon arriving at the institution, the Dark Knight discovers that the Joker has already escaped. Elsewhere, the Joker kidnaps Commissioner Gordon and shoots his daughter, Barbara, in the stomach. The bullet hits her spine, causing her to be paralyzed from the waist down.
The New 52 And Batgirl's Recovery
By the New 52 continuity, however, Barbara is back on her feet and fighting crime as Batgirl once more. This led to some concerns that DC was turning away from one of its most famous disabled characters. This led to confirmation that the events of The Killing Joke, including Barbara's paralysis and time working as Batman's hacker Oracle, are in fact canon in the New 52 continuity. After working as Oracle for a time, Barbara was able to undergo a form of physical therapy which eventually allowed her to walk once again with the help of a technological implant. The justification for her return to crimefighting in terms of storytelling was simple: she was the most famous iteration of Batgirl.
While this has been faced with the aforementioned criticism, Barbara's paralysis was also faced with scrutiny to begin with. Some critics claimed that immobilizing Barbara Gordon did the character a disservice, especially when Batman himself famously had his back broken by Bane and was able to recover without being confined to a wheelchair for a significant period of time.
Gotham Knights takes place in its own continuity entirely and is not related to the New 52, no matter how much inspiration it ends up taking from that run of comics. It is likely that Barbara's paralysis will be canon in her backstory, however, with a unique perspective and an explained recovery. Batgirl's in-game abilities include hacking technology to create environmental weapons, which also makes it seem likely that she's already able to draw on her experience as Oracle.
It's also likely that technology will be behind her recovery in some way, with the Bat family clearly having access to extremely powerful tech. After all, one of Robin's abilities includes using the Justice League satellite to teleport across short ranges, so Gotham Knights clearly takes place in a tech-heavy version of the Batman universe. Either way, Gotham Knights will need to ensure that Barbara's recover is dealt with respectfully, and is an important part of her character and perspective instead of simple a part of her backstory that risks getting swept under the rug.
Gotham Knights is currently set for release on PC, PlayStation 4, PlayStation 5, Xbox One, and Xbox Series X in 2021.