True! She’s really a bad person but you can see where she comes from, and she’s so convinced that the evil she’s doing is to ultimately protect Harlem, that you can’t convince her to stop.
What is also interesting and touching is that, despite not loving Tilda (and tbh who can blame her for that, it’s really sad for Tilda but we can understand Mariah), she still genuinely cares about her. Up until their breaking point, she always told Tilda she loved her, because she knew a child always needs to feel loved. She was a distant mother but she always tried to make her daughter feel loved. She didn’t tell her the truth about her origins and about her feelings because she knew it would break Tilda’s heart and she wanted to protect her. Of course, when Mariah finally broke and embraced her evilest self, she eventually broke Tilda’s heart. But as you said, it was her fucked up way of “helping” her daughter : breaking her heart so badly that no one could ever hurt her that bad again.