I don't really understand what a "random encounter" between these two actually constitutes. Like, the premises for the fight. But if they both enter this abandoned city with awareness that they will encounter someone and are supposed to fight, Laura would be able to smell Bruce, track him, and analyze him from a distance, ensuring she was not within range of him until she had figured out how to take care of him.
Batman has so many ridiculous feats that I'm sure someone can and will come up with a grand narrative for how he beats her, but with no prior knowledge of X-23 before the encounter I really don't think he should stand a chance.
*goes back to avoiding battle threads*