There are 413 total villagers in New Horizons as of the update. That means that everytime you go to an island, there is a 0.7% chance that she finds one of those three villagers. The odds aren't in her favor. No villager has a higher or lower chance of spawning, no matter how much you might feel like some appear more than others.
It's just bad luck. I used 150 NMT's before I ended up just having someone give me one of my dream villagers way back in the day.