@JonHig,
I think you hit a site hiccup. No worries.
It might not be a broad enough topic for a thesis. Plus a lot of it's speculation. Hmm.
Your email notifications in other areas of FB would not be affected by this.
I am getting the feeling that the account is either set to private or a restriction was placed on postings, where they're going out to everyone but a small # of people, including you. Possibly both.
FB settings are numerous and so it can be hard to get a handle on what a user has done.
Truth is, though, reading between the lines here, I suspect it's more of a relationships issue. See, I know what my husband's settings are on FB or at least I have a good idea, as his account is open and visible and he's easy to tag, I see what he does, etc. We are both friends with people from our past and nobody bats an eye.
But if your wife's FB talking, posting, etc. with someone else is of concern to you, then you'll need to talk to her. That goes beyond online settings, and into what's going on with your marriage.