curley's right, OP can't simply deregister the wife, he needs a power of attorney to do that or a judicial verdict.

That's not what you did, you merely stated that her address is no longer valid. The clerk's reaction. assiing the gf was indeed deregistered, was an indirect consequence only.

OP can't deregister the wife. But he can inform the authorities that she left the country for good. Under ordinary circumstances her permit would lapse after 6 months so she automatically would be deregistered. The extent to which this applies to such a case, as it's about the marital home which enjoys special protection, is to be seen. But short of seeking a judicial verdict that's what I'd enquire about first if I was OP.

As sad as it is, I'd use access to a bank account, or monetary payments in general, to make her cooperate. Just make sure you stay in legal territory, by all means avoid what could be seen as coercion.