Could Alice, Kate Kane's emerging nemesis on Arrowverse already has been.
Following her brief appearance in Elseworlds, Rose returned to headline a solo outing. Alice and her Wonderland Gang. The episode ultimately revealed that Alice was actually Kate's twin sister, Beth. Following a childhood car accident, it was believed that Beth had died. In actuality, she had miraculously survived and instead forged a path to villainy.
The details of that journey are currently shrouded in mystery. Given that she was just a child at the time, the scenario poses a slew of questions regarding how she not only survived the initial crash but also lived undetected for decades and ultimately amassed an extensive network. The Monitor having a celestial hand in proceedings would certainly solve some of those conundrums. At the time of the crash, Batman arrived on the scene and seemingly secured the car from falling off the bridge. Unfortunately, the cable snapped and the car plummeted anyway. Batman was haunted by what happened and was still investigating what went wrong right up until his disappearance. Though it was ultimately blamed by Luke Fox on the car's flawed craftsmanship, that felt too simple for a mind such as Batman's to not for. Besides, there are rarely coincidences in the world of comics. The Monitor would certainly have the ability to pull off such a deed under the nose of the The World's Greatest Detective. Equally, he could remove Batman from the board altogether should he prove an obstacle.
That's not to say she was raised by The Monitor, similar to how Arrow that looks increasingly based on falsehoods.
When it comes to preventing Crisis on Infinite Earths, there is nothing The Monitor wouldn't do to ensure his apparent plan. All the while putting his chosen heroes through trials by fire. Unlike last year, Batwoman is set to play a central role, making her definitively one of his chosen - even over Batman. As a result, he would have to ensure that not only is she worthy but that she's shaped to the exact specifications required by his plan. Causing the inciting tragedy of Kate's life would fit this M.O while also not overshadowing Alice as the season's Big Bad. Conversely, it could add a new sympathetic layer to the villain. Such revelations would also put Batwoman on an even footing with the heroes who've already been influenced by (and will no doubt be angry at) The Monitor. Equally, it would allow Batwoman's post-Crisis back-half to focus more on its future rather than the questions of the past.