So just what was Belial's plan there?

[Elric of Grans]

There is a reference to witches being treated as criminals and a very clear stigma against them. They do not seem to be considered good things, so it makes sense that Leah would not want to think her mother is something horrible. Cain probably told her stories about how kind and gentle her mother was as she grew up --- the usual trash you tell kids.

Skyrim is another example of what Bolty is talking about. You can go on a murderous rampage, but children cannot be harmed. It would make for a better story, but the media would have seen Blizzard shut down over it. Making it talk only completely loses the effect, so what they went with was just as good.