What a great forum. It definately is now a bookmarked page!
Though like everyone else, my interpetation of Sedna is preliminary, I believe Sedna relates to a.) the failure of the parent to provide proper guidance and or support (spiritural as well as physical) in the development of the child. b.) the result of that abdication of responsibility.
In Sedna's own story her father allowed her by his indulgence to grow into a self absorbed young woman, than cast her off as soon as he decided he could no longer feed her.
As the result of Sedna's upbringing she had no clue on how to successfully secure a husband. She fell for the trappings of wealth, without looking inside to see what her potential husband was about.
In a person's chart, where Sedna falls shows where the parent failed to nuture. It shows where an individual's awareness of the proper way to handle the affairs of that house is warped by the parent's inability to guide and teach.