Remember one thing, whenever a teacher applies for these types of special leaves (like B.Ed. on deputation) he/she passively refers to a date on which he/she commits to resume his/her normal duties to the school. Not only that but also a certain resolution is taken by the M.C. which is thereafter sent to the D.I. for further proceedings. It means a teacher enjoying Maternity Leave is committed to rejoin the school after the expiry of allotted six months of Maternity Leave. On the other hand there has recently an order for the release of teachers studying B.Ed. on deputation been issued though. But no such order for the cases of Maternity Leave has been issued as yet.
Remember, a teacher is always on liberty to join her duty on any day before her Maternity Leave ends. You should,of course, release the teacher who is on Maternity Leave, if she applies for Release Order. But her Maternity Leave will end as soon as she joins school and she will not be able to enjoy the rest of her Maternity Leave once she joins her duty.