User blog comment:Blaziken rjcf/Why God created the Leviathans/@comment-1975828-20160614103644/@comment-1975828-20160615022805

In terms of canon information, God created the archangels to help imprison the Darkness, so we can't say for how long Amara existed alongside the archangels. It could have been as short as one day, two weeks, or four months. We don't know.

It's implied that Lucifer helped God trick Amara into being imprisoned, which is why she knows him so well.