But she ended up recruited; the teens are too young and have too many outside connections for that. But neuralyzing the first humans to bond with the Autobots would be a stupid move on so many levels and unlike Sector Seven, MIB is smart enough to avoid doing that.

The cartoon had one case of a human woman who (unknowingly) married an alien, but who was shown to not be neuralyzed after she found out. (There's also an early episode where a kid bonds with an alien who crash-landed on Earth, and even though J named him an honorary MIB, he was still neuralyzed... though in that case the alien was evil and playing with the kid before eating him.)

Er, to sum up, MIB figuring out how to handle the situation would be a major subplot in and of itself, which would distract from the Transformers conflict possibly in the same way that the movies' human subplots do now. It'd make a good crossover movie, but maybe not a better TF movie. (BTW, what I'm picturing now is a scenario where MIB takes over from Sector Seven after the first movie, as if the universes suddenly merged at that point. I haven't gotten past Zed's epic headdesking over the unholy mess that just appeared in his lap.)