It is hard to control blushing, it comes from the body not from the brain.
That is why Daria is soooooo *cute* when she gets red. It shows, how her body revolts vs. her controlling mind. That has IMHO a very nice symbolic meaning. To show us that Daria in the end, belongs to the human race.
Did somebody out there, made a siencetific analysis about Daria's blushing record.
I mean: She blushes a lot in season 2 and season 3 because, Trent, Ted Devitt-Clinton and her parents.