Can I ask if how much the discount about overstay...

We would like to inform you that your question is not related to our field of work as legal consultants in the legal department. We are specialized in providing legal advice to our clients.

In addition, the site does not have any relation with any government or private entities
Concerning your inquiry,

It should be noted that after reviewing your inquiry and legal scrutiny we would like to inform you that concerning the fines for overstaying in UAE waiver, it depends on sole discretion of immigration dept of the respective Emirate of U.A.E.

You should approach the immigration department, and submit a request letter typed in Arabic asking them to waive your fine and wait for their response.
Because it is the only way to waive a fine and you do have to explain the situation clearly and present the given VISA to show that your wife is in legal situation.

In the event that the intended question is otherwise, you can kindly ask us in detail and we will respond to it in the shortest time frame.