Try the Glassdoor website. I think many of the jobs are advertised there. Or many of the international schools recruit from the employment fair's that are held in various parts of the world. Otherwise, she could apply to be a supply to get her foot in the door and work from there. I'm not a teacher but a parent from an international school and this is my understanding. Maybe a teacher could give you a better insight.

My wife is a recent graduate of Auckland University secondary teachers diploma specializing in science (Biology).
With 30 years bench science in Asia/UK/North America.
Her preference is working on the UK/Cambridge system
She is Singaporean and we have a landed house available on the east side,

I work from home on ICT research and development
Prefer public transport due to eye injury (recovering after 2 years of operations)

Daughters in Year 13 and Year 8 (Both in Cambridge system)

Thinking about a move to Singapore from Auckland,

Any words of wisdom?