In a good and big organization, the performance appraisal system and process do not get affected by an individual on maternity leave. Thus, if the absence is during the performance period, then the last or average ratings are prorated for the period.
Similarly, the date of increment is uniform across the organization and for all employees. Therefore, the date of increment will remain the same. The employee will receive their salary or leave with wages accordingly. This is the general policy in good and reputable companies.
However, small companies or those with dubious policies may adjust this according to their requirements.
Warm regards.