I would actually really like it if your theory is true, though really dark I find it too interesting to reject it;
Mama killed herself for Laharl and unknowingly kills her unborn baby in the process? Damn if she knew that, her heart must have hurt like hell, no wonder she never told anyone who she really was, she must have felt so ashamed of herself.
If you are right, Sicily must have never met Mama either, poor thing.