Green Bell - Correctly predicts the relative order of 3 racers
Plum - If her prediction misses this time, she'll be correct the next time she predicts
Nazuna - At least two out of the three racers she marks will be in the top 3

According to Green Bell, x20 will be above x30 and x10 in the final results, making this racer a probable winner.
Plum's interesting new mechanic doesn't make the prediction easier, though it may help out next time.
Interposing Nazuna's prediction on Green Bell's, we can say that x10 will be outside of the top 3, so x20 and x100 should be in it.

A bit uncertain for the first race, but any of x20, x50 or x100 may win.

RESULTS: x20, x50, x30, x100, x10

And with this, we need to update Nazuna's predicting habits as x10 and x100 took the last two places. Is it really random? I can't update it to "at least one of her predictions will be in the top 3", since that's obvious with her marking 3 racers each time.
Since Plum's prediction was off mark, the next time she appears she should have the deciding vote.