There are two cases:
First Scenario: When the sponsor is not pleased with the maid...all they have to do is just take her back to the agency and they will tell him what to do. Usually they just give him another one if they are still withing the warranty period...if not then he will have to release her to another sponsor... and off course they will figure out a way to charge him extra money...they are high-way-robbers.

Second scenario: When the maid is not pleased with her sponsor...usually, this is a blind-end road for her...still no law protecting the maid or backing her up unless she's got a real issue.
That's why most maids try to make up tragic stories in order to get their freedom, some of them claim abuse (sexual or physical)...others claim they don't get paid...and so on.

My advice..if you have a maid who is not under your sponsorship...just give her back to her original sponsor or you make arrangement with him to give you a release...otherwise...you might get yourself into an illegal situation