Responses
We don't know yet if that's the case. What we know by what Tian Hu said in the first episodes was that everyone misunderstood MeiLi's mom for being the mistress of Tian Hu's father, because of that, Tian Hu's mothers hates MeiLi and his mom.
But in episode 28 we have two options:
1. The evil woman killed MeiLi's father because he knew about all her wrongdoings, he was getting in her way.
2. She was secretly in love with MeiLi's father.
I think is more like the first option, but we don't know yet what exactly happened between them, or why exactly she killed MeiLi's father.

If she was in love with Meili's father, then she lost her crush to another woman, lost her husband to the same woman and lost her son to the son of that woman. Quite a miserable life. But I don't feel bad for her. She is evil.