“It is permissible for the husband to designate a representative to divorce his wife whether the person is a stranger or even the wife herself, as it is permissible for the husband to authorise his wife to divorce herself.”

What does this mean?

In Islamic family law in the chapter of Marriage and divorce there are certain instances the husband can do certain things through a representative. One of the things that he can do is to divorce his wife. The pronouncement of divorce comes from the husband and then the representative will then deliver/convey it. The husband can also tell the wife that if you do such and such a thing, then you have the right to divorce yourself. All this is what is meant by the statement.[1]

Reference:

[1] Sheikh S Al-Fawzan, A Summary of Islamic Jurisprudence, 2/430