Yeah, her dad lied about what happened to mom. I might too in that situation. "Oh no honey, your mom's alive and has been the mistress of our planet's evil overlord... oh it's evening at Terok Nor standard time now, she he's probably banging her right now."
Not only is a noble death a bit more... merciful... on children's ears, but what was Kira's reaction when he learned of it? Oh yeah, she was a collaborator and deserved to die. Maybe he didn't want their kids to hate their mother.