You've damaged them enough

It wasn't like Hera didn't understand Old Madam Zhu was simply trying to prepare precautions. After all, the person the latter was expecting to target her was Hera Cruel. By telling Dominic, even if Old Madam Zhu died in Hera's hands, Dominic would know who killed her and what sort of enemy might attack their entire Zhu Family. It was something anyone would do in such a situation.

The problem was Dominic and Hera already knew each other. 

They knew each other so well they wanted to spend the rest of their lives together. Hence, instead of understanding, Hera simply felt choked by Old Madam Zhu's actions.

"That I killed a friend. Your mother. I also told him about you. I did it with the thought you would not listen to a word I said. So, he knows who he will deal with in the future."