Sigdi vs. O-Chul

[Grey_Wolf_c]

she could have emerged fully-formed from the head of Zeus (okay, not OOTS-Zeus, it's an expression) for all we know.

"Could have" is a far cry from your original assertion "Sigdi is the way she is purely because of her own will." (emphasis mine)

You don't know that she is that way due to her own will, and thus bringing it up is indeed assuming a fact not in evidence.

Grey Wolf