Kanna was masquerading as Koharu's classmate in her flashback, though I'm sure in her case her aim was to make her fall in love and Koharu's death was a genuine accident she was powerless to prevent. Here though, it certainly looks like Sae caused Ena's death on purpose.
Personally I don’t think it was a genuine accident. I think Kanna got into a fight with another Cupid and that’s what caused the debris to fall. That’s why, in Ch.5, Chiyo says her reputation is that of someone who runs from fights. She’s seen firsthand what careless fighting between cupids can do.
If I’m right that could also provide an interesting bit of conflict between Kanna & Sae. Both are responsible for the birth of a cupid. But where Kanna sees it as a mistake she must atone for, Sae deliberately engineered Ena’s loveless life.