I'm not sure if the pixie itself really needs to be champion; I haven't thoroughly tested that myself. The main thing is having the pixie on the farm during the yearly examinations that Talt starts doing.
I'm pretty sure the event will only trigger once the 'story' of the examinations is otherwise done - so it probably can't happen at all the first few times when the doctor is going with and overseeing Talt on her rounds. Maybe not even the time after that since there's still some dialogue about here getting used to doing things alone, but I'm less sure there.
Again, I haven't done full testing myself, but I recommend casually raising some other monsters for cash or other unlocks or whatever until all those events pass, then bringing out the pixie for the next examination after those, see if that works out for you.