I may be off, but Saturn in 12th house could signify the parent who at the time may have had trouble with responsibility during the pregnancy. Jobs, career sacrifices, chronic health problems(Saturn = bones, old age, crystallization), fears of being chained to a responsibility or even commitment, I don't know, the list goes on... I notice many people with Libra in 12th have parents who were split up or couldn't stay together for one reason or another. Thus, relationships of any kind are very hard in this lifetime and thus, the native often makes up a great deal to heal the wound. The native has that lesson or gift to keep this intact in their future relationships, or come to grips that sometimes they are found alone or feeling very lonely, unrecipocated. Possibly a fear of divorce, and no doubt being or dieing alone.
Sun in 12th house? Maybe the ego is denied. Usually someone who cannot stand up theirselves, usually wandering around being pushed by stronger personalities(1st house Suns?).
I always think gifts of the 12th house is a vast reservoir of spiritual, psychic knowledge or lessons learned/gained through the conditions we either imposed it on ourselves or we were limited upon in the first place. I think atonement is a good keyword to describe this house experience as well. You make up for something that you've been heavily denied, this is why sometimes spirituality is often found in this house... our experiences are not normal compared to others, sometimes illness or health difficulties or something equally difficult that keeps us in check, forces us to step aside and come to acceptance with such hardship.