Apple ID Email Address Change

My wife's Apple ID uses a defunct email address for her ID. I want to change the email address to the one she currently uses.

I have read that this process can be troublesome, yet Apple's advice makes it sound quite straightforward. Does Apple send verification advice to the old address? If so, it won't be seen because the address is no longer active.

I would appreciate any advice on this subject as I don't want to mess up the Apple ID.