Need your help here! One of my friend is holding WP and she is already tender her resignation letter in a proper way which is served notice for 1 month. But when comes to her last day of work, her employer refused to cancel her WP pass and insist her to cont' work with them.

My friend already get everything prepared and need to go back her country but due to her employer refused to cancel her WP pass, now she is still holding WP pass .
During her absent ( her employer rather called it as long holiday),the employer still will pay for the levy fee and hope that she will come back like 2 or 3 months later.
She is planing back to singapore in future for a new job.Need your advise on this, how exactly my friend can cancel her WP without being blacklist or slander by her employer? Can she report to MOM regards this? will it affect her next job? Many thanks!
Regards,
Lav