Mary wouldn't even harm a fly. How could she commit such a crime?

玛丽心地非常善良。她怎么可能会犯下这起案子呢？

So, if someone is very gentle with no violent feelings at all, we could say that person would not harm a fly.

所以，如果一个人很温和，没有任何暴力情绪，我们可以说这个人不会伤害一只苍蝇，十分善良温柔。