When you look at her profile do you see the things she has posted that are for friends only? Or just the public things or nothing. If you see public/nothing and are her friend still then she possibly has you on "restricted" access which is in the blocking section. If you see her stuff that's set to private friends only then you see what all her friends see.
I also have my friends list set to only me. Only bc I have family members who get upset if I'm friends with other family members. Hide my friends list, problem solved.
I do want to say there is a way you might be able to pick and choose who can see BUT I'm pretty sure it's just these options- public, friends, friends of friends, only me. I choose only me.
You can only see comments on mutual friends posts based on how her settings are and the friends. Typically anyone who posts a public post and a friend likes/comments on that it will show up on all the friends newsfeeds.
I would think that if she were up to something she would just set a fake fb?!
Ok and last thing- there is an option to set up groups so that when you post things you can have only the people in this group seeing and commenting on the post. It's not called a group it's something else- friends list maybe? Maybe she has that and you aren't included. It's under the friends list and if you ever see someone post a status and next to it shows where it's public of friends instead it will show like * an asterisk or something that means that status was shown to a list of friends not everyone.
What I would do- get in her fb and screenshot her friends list, see if she has people blocked- screenshot that, and see if she has people on restricted and friends lists set up. You need to get in her account and look for those things and well obviously messages and stuff.