Your wife should talk to a manager or even her HR rep at her job. This is a serious issue that has to be dealt with and can not be left alone.
Doing this will only help her and that employee will stop verbally abusing her. If this does not help, maybe you should consult with a lawyer but this...
I really think that what ever the doctor says in terms of how many days your husband can work, this should apply right away.
If his doctor says that he is able to work 3 days out of the week, then this should be the days that he will be working.
But if the doctor says that he is able to...