Originally posted by Glenn
I would phrase it that way as well, but I find this interesting: using "ni" in this sentence seems more natural to me (although I am a non-native speaker, so take that for whatever it is worth), but saying "Keiko e no tegami" for "a letter to Keiko" is perfectly acceptable, and I believe more common. Perhaps it has something to do with "no" overriding "ni" in these situations...