From India, Salem
There is no law governing this widely followed practice of giving yearly increment to employees. It is entirely left to the company.
The increment generally becomes due on completion of one year's service .
One of the crucial factors considered is attendance and days worked together with performance during the year. Your wife has worked for 9 months and proceeded on ML.
She has not completed full one year's service and it is management's discretion to grant increment or not , fully or pro-rata and give now or after resuming her duty.
From India, Mumbai