While it was rare, the accidental casting of spells by Ellen as the result of a sudden sneeze could still occur.
Weirdly, this was more common when Diane was around, and that's not meant sarcastically. Ellen had no intention of accidentally zapping Diane, and there was no outside reason why Ellen would be more prone to accidentally zapping Diane.
It was simply a statistical anomaly that Diane had gotten somewhat used to, along with requesting funds should any attire require replacing.