In the Spellsong universe, it was very difficult to send a scroll, though scrying was much easier. Why did they not write a message on paper and let it be scyred between sorceresses? They could then communicate back and forth much more easily. And so it wouldn’t be seen by others keep in in a location not near the author and also remove it after a set time so it would only be visible for a very limited time.

First, there aren’t that many sorceresses who can do that. Second, for something to be read, the letters would have to be made large enough that only the simplest messages could be conveyed. Third, an unfriendly sorcerer or sorceress could also observe such a message.