I like Seraphina and I sometimes play around with the idea of using it as a middle name. My favorite combo so far is Alice Anna Seraphina.
I'm not sure Sadie would work. It starts with S just like Seraphina, but that's about it. What about Phina or Phee?
We’ve all got both light and dark inside us. What matters is the part we choose to act on. That’s who we really are.
PNL: http://www.behindthename.com/pnl/45898
Top rated: Helena and Henry
Bottom: Farren and Amandus