Personally, I am not 100% convinced that it was really Lord Raith who killed Maggie Sr. Sure, Ebenezer believes it, but then he may well be blinded by his prejudices -- automatically blaming the "drug dealing scum of a boyfriend" for her death. We don't really know recipe is required for birthing a Starborn, but the fact that Elaine (known potential per WoJ) is also an orphan suggests to me that we can't rule out death during childbirth as being one of the ingredients.
1) IMHO it is not impossible that Maggie killed herself deliberately to create a Starborn.
2) It is even possible that the mother needs to die with an entropy curse in order to create a Starborn (HHWB-Entropy curse connection in Blood Rites). Maggie could well have done this to herself.
3) Note also that technically it was Maggie's Death Curse that killed her.
Still, to me this whole planning ahead to produce a Starborn, while I agree that it is a strong probability, has one anomaly -- Thomas. If the UMO Alliance, Lord Raith and the others all planned ahead to create a Starborn...Thomas should never have been born. I love Thomas to death, he's my favorite next to Harry, but his very existence makes no sense.
How do you suppose Mab reacted when Lea told her, "My Queen, I know we have been working with Margaret LeFay to produce a Starborn, however It seems she has not stuck to the plan."
Do you think Mab, or Odin would have been thrilled to learn Maggie was pregnant with a 'Bastard' child?