I always found it odd they felt the need to somewhat retcon her death that is mentioned in 4 when it isn't in the continuity of H20. I suppose it was the hardest detail to ignore, but they had no problem erasing her daughter from existence.

Ah I misunderstood what you meant by "scripted premise" as I would consider the treatment the first stages of a scripted premise.

Not true. Originally there were nods and references to 4-6 in the script.