Yes, she will continue to receive benefits from the ESIC until her benefit period ends. If the benefit period ends before the maternity leave ends, then she will have to provide proof of employment. Obviously, if she is covered under ESI in her new employment, there won't be any issue as she will then be considered an insured employee under ESI.
Challenges in Transitioning Employment
However, the challenge arises when there is no proper transition from the previous employment to the new one in terms of marking the end of employment. This can cause difficulties in registering for ESI benefits in the new employment. From an ethical standpoint, it is not advisable to join a new organization while still being employed elsewhere. Employers should not encourage or entertain such practices.