Cocoa encounters Syaro handing out fliers for her part-time shop. Syaro says she cannot return (to the shop) until she finishes handing out all the fliers.”

シャロ：

「全部(ぜんぶ)配(くば)り終(お)えるまで帰(かえ)れないわ」

In this sentence, 終(お)える is used because Syaro has to put in effort to complete the action. Rather than “when I finish handing out these fliers”, it has a connotation of “when I manage to finish”.