Change your passwords.

Mutual friend (you think s/he's a friend anyway).

Are you reading her stuff? Stop it.

are you or your husband friends with Skids? if so, even if all privacy settings are correct there is no stopping BM from saying "hey susie, show me whats on your dad's/SM's pages".

phantom accounts. I have one w/some random name that isn't even close to my own name. I use it to look up old boyfriends, neighbors, co workers, etc. If you don't know what name I made an account under, you can't block me.
Look carefully at your friends list and delete anyone you don't talk to in real life.

change your passwords as well...just in case there was some way of figuring it out.

Go into your facebook settings, delete all devices.

Check and make sure facebook has YOUR cellphone number/ email address as the conact number.

Change settings so anytime new device is used to log into your account facebook text messages you a new code so you can access your fb accout from the device.

Resign in your computer/ cell phone (your normal mode of using facebook)
Sit and wait, if you randomly get a text from facebook with an access number you know she had/has your password somehow.

Click on your keyboard
ctrl+alt+del
open task manager

under processes tab see if there is a keylogger running (one way for someone to get your password and you were the one that typed it in)

Or:

You can have fun with her.
Make a post that you won $250k in the lottery.
Watch how fast she files for a CS increase/ alimony increase or how fast the skids start calling you up for $$ for stupid shit. When dumb a$$ requests for cash are made, snort and ask them

"What do you think we won the lottery or something?!"

Profile pics n cover pics are public !!!

It's insane that people stoop to stalk ~ why in the world would you care what I do ??? Simply reason ~ curiosity ~ but didn't curiosity kill the cat !!!

Honestly at this point I think I'd delete my account and create a new one. Or even keep the old one (don't use it) and create a new one anyway. Add your friends back to the new account one at a time and see if BM suddenly gets access to your pics when you add someone.

Edited to add: Oh, and I think you mentioned that none of your friends are friends with BM, but maybe one of them is friends with one of the skids? If so, then BM could see your stuff through the skids account. (Although I think you can lock down to "Friends Only" versus "Friends of Friends" - might want to triple check that you don't have that set up on your pictures.)

I had a cyber stalker for a while.

The best way to beat them is to simply go off-line for a while. I've done this with FB, and some other blogs. My account is still there but I am just inactive. Eventually the cyber stalker gives up and just moves on to someone else to stalk. It worked like a charm for me.

BM in my case set up a new account for SS and sent me a friend request. I actually was happy about the request and accepted it right away, without thinking. A few hours later as my DH and I were eating dinner, I asked him if he had received a friend request from SS, as it appeared he had made a new account; he had not. SS was very, very rarely on facebook. I also noticed that none of his cousins or aunts and uncles or even BM herself was a friend. Boy, did I feel stupid for believing it for even those few hours. So "SS" was unfriended. There was never a word said about it from or to anyone.

It somewhat amused me to think she was interested in what I was posting. First of all, at that time, my posts were mostly public. Since that incident, I've changed that so my posts are for friends only. I figured if she couldn't get enough of me with public posts, I'd really drive her nuts with hiding stuff. Absence makes the heart grow fonder, right? Ha.

If you google the persons name it will pull up thier Facebook account. Even if that person is blocked. I did this when I wanted to look at BMs account but she blocked me (i know, I know, shame).

Let me explain how she is doing it:

1. She will need to sign out of her account - that way her computer does not associate that it's her
2. Then she can google your name or screen name
3. Pull up your account

As far as her being able to post to your account - no idea. I only got a B in my IT and computer classes.

I leave everything public now, so the miserable BM can see how awesome my life is }:)

But if it bothers you - I agree with the rest. She must have a fake account somehow and able to see anything public or "friends of friends' of yours. And perhaps your page isn't as private as you think? FB profile pics automatically set as public now, so make sure you change the settings. I would just look at all your settings again