Astarte doesn't care where she came from. What use is knowing such a thing? The old Universe is gone and nothing done in it matters any more. It's best to just start from scratch and prove yourself to others instead of telling stories that most everyone else will think are fake.

Edit: Also, can you imagine how powerful a God Soul is? Picture Astarte getting the help of Vestec and stealing someone's soul. That could potentially be used for really destructive things.