“If the maternity leave availed during the probationary period is counted as service”-Yes.
“does the probationary period extends for that particular period?”
It should. The probation period is the period kept by employer to observe the employee and decide whether the employee is fit to be absorbed in establishment as confirmed employee or not.
The authority empowered to recommend confirmation of service would also consider the eventuality of decision becoming and being quoted as precedence.
The authorities may also look into if the performance and contribution of employee is exceptional and the employee is indispensable for the organization and any other factor that they may deem to be fit.
Law would lay guidelines on what is the minimum to be given and nothing stops an employer to give more.
As per rules applicable to your establishment the period of admissible leave is 180 days and then there is 730 days (2years) of Child care leave. It is a big period.
Valuable advice of learned experts/members is sought.