Thanks for your responses. The situation is that my sister is in TLV on a RTW, and was cheduled to fly in July TLV-VIE-SIN on OS, and SQ SIN-MEL. But my brother got engaged, so she's coming home early, as in January. It being the school holidays/summer in Australia, SQ is full every flight, every day. OS though has availability on its thrice weekly VIE-SIN-MEL flight, so I want to book her on that.

thanks again,
goodo