お姉ちゃんが振り向きざまにきっぱりと言い切った
Big sister turned around and ?? clearly asserted...
From the answer on this question about ざまに, I understand ざまに to mean "while". But in what way does it differ from ながら? Is it only used in writing? Is it more formal? ... etc? Why would I choose one form over the other?
～ながら is like "while", and ～ざまに is more like "the (very) moment~" "just as~". You'll see it in (set?) phrases like 「すれ違いざまに」「追い抜きざまに」「追い越しざまに」「振り向きざまに」 most of the time, at least in modern Japanese. You wouldn't rephrase them as すれ違いながら, 追い越しながら, etc. (These would make sense, but the nuance may be a bit different). You would say 「お茶を飲みながら」「テレビを見ながら」 but not 「お茶を飲みざまに」 「テレビを見ざまに」 etc. I think the verb before ざまに should probably be a momentary action.
(By the way, 続けざまに is a set phrase meaning "(do an action) in a row.")
