I know
Theodora gets
Theo or
Thea from a few people but it seems like you've mostly kept the use of her full name without nicknames?
Seraphine or
Seraphina could be the same.
What about
Seraphine or
Seraphina with the nickname Rafi? Or Raphi? I saw your post about
Raphaela but I think
Seraphine or
Seraphina is a much better match with
Theodora :)