Well, you sound like me before I lived that. Trust me that I could give you my FAcebook -open account- and judge by yourself the amount of personal details I give there.
The key was that she added me to her Close Friends list, without me acknowledging that, but what did I know? That sounds pretty pretty cool at first, even if she told me I'd be so happy knowing that, it makes you feel exclusive.
In fact I added two friends of mine to my close friends list the first days I joined Facebook on Dec 2011.
To me it was one of those things that go overlooked, and in fact I added them to the list to have someone there. Still I didn't notice what was the purpose of that.
So.... thing is... She used that to know to whom I gave *likes* and read ALL my comments.
It felt quite surprising at times that she liked some comments I made in Facebook accounts from certain corporations, talking about DVDs, or CDs, or Windows, or Google, or whatever...
I was like... How the heck did she read that to give me a like? I blamed it on the status bar by the right side of the screen, which gives you -mostly unnecessary- information on what people on your FL are doing.
So it went unnoticed for me. But then she began to control everything people said or did in my Facebook account. "Huh? Your sister-in-law gave you a like for this, but she didn't give you a like when you mentioned me. " Things even escalated and she wanted me to distance from my family. I love my family, whether it's less or more perfect, so...
That was the last straw. Still I am surprised at what happened.
I ended up outsmarting her several times at the end and found out that if you add someone to your close friends list you can basically know every single activity of that person on Facebook.
Fortunately for me, I used Xbox Live for social networking sometimes, which is much more private. She even wanted my email password and told me that she would pay me a year of Xbox Live if I gave her my Live account password, to know my interactions with people there. :/
She didn't even know what a Xbox is nor what Live is, and that increased her curiosity. She knew some of my FB friends are also friends on XBL...
Anyways, your approach on FAcebook sounds interesting for me, it might be useful for future interactions.