Just get her user name and password and check everything out. If she refuses to give it to you, this is a big red flag. I for one would not put up with it - we would have a MAJOR PROBLEM.
I agree with this. There should be total transparency in a marriage, especially when it comes to online interactions. And I'm not even a paranoid dude.
She probably does have her privacy settings so that nobody can see her friends list, however that's usually reserved for "friends of friends". If none of her FB friends can see who she's friends with, that's something she knew she was doing, not a suggestion from FB.
FB WANTS people to connect. They're not in the business of suggesting their users lock down their accounts, regardless of whether it's possible or not.
If she has made her privacy settings universal, that's not necessarily indicative of her hiding something from you, specifically. Often it is the easiest way to set them - lowest common denominator, applies to everybody.
However, she CAN set individual parameters for people like you. She can go to your page, and set you as a "close friend", which means you would each be able to see everything on each others pages, including friends lists. It would also mean that every single thing each of you posts on FB would show up on each other's feeds.
FB currently employs algorithms to pick and choose what people see in their feeds, essentially taking a guess at how often you want to see posts from friends. They depend on how often you communicate with each other, how often you "like" something somebody said, etc. Making somebody a "close friend" over rides those algorithms, and shows you everything, regardless of whether you actually chat, like or generally communicate with that person.
I would suggest you ask her to make you a "close friend" on FB, thereby allowing you to see everything.
If she refuses for some reason, then you'll know she knows what she's doing on there, and not just following FB's "suggestions".
If she agrees, then I imagine you'd have nothing to worry about.
Problem solved, without having to be sneaky about it.
OR... if she ever leaves her FB open, go to your page (via her account), and where it says "friends", a drop box will open, and you can select "close friends".
In addition, you can (via your FB account) go to her page, do the same as above, but also open the box directly next to that one, and click "see first", so that her posts show in your feed at the top.
*ETA - conversely to the above, she might very well have specifically set you (and maybe some other people) as "acquaintances", which does the opposite of making one "close friends". It effectively maintains you as FB friends, but without revealing all their info (including friends lists). I suppose it's possible she's done exactly that. I doubt it, but you never know.
Again, you can check her settings should you ever have access to her account, with or without her there. Just ask her to go to your FB page while she's logged in. It'll still say "friends", regardless, but if you hover the cursor over that box, it opens the drop down box and a check mark will be next to whatever designation she's given you - close friends or acquaintances.