Well, Veronica is pretty unique. You never actually race her, you try to beat her best time, while the game simply plays back a ghost of her (presumably a race some developer did) in the same way it plays back the ghost of your car if you choose to race again upon finishing a time trial. With that said, I'm pretty sure Veronica isn't actually coded into the game as an NPC in the same way the other NPCs are, and most likely cannot be placed as an NPC in normal races because she doesn't exist in the game's library of NPCs.
To be more specific, the other NPCs actually interact with the player and track, using power-ups and making semi-random route variations and such. They're AI-controlled opponents. Veronica only appears as a ghost, and like a player ghost, always takes the exact same route around the track, and cannot be interacted with in any way. Even if you go ahead of her ghost in a race and steal all the power-ups before her ghost reaches them, the ghost still "gets" them and "uses" them in the exact same location each and every time, even going through shortcuts you may not have opened yet. She's a built-in ghost that was recorded by a developer back in 1999 - not a true NPC racer that makes its own decisions on how to race in real-time.
Please feel free to prove me wrong though, as I'd love to race against her on the Rocket Racer Run.