Sharing is simple.
Where it seems like your complaints lie are in getting too much information - above and beyond what has been shared.
To me, I suppose that's small potatoes. I get the occasional distraction in my stream, but Google's usually smart enough to make it relevant, and about half the time I see something from outside of my circles, it ends up drawing me into a conversation.
I am decidedly not your mom, and I don't mind it. Also, my stream is active enough that those 'outsiders' ever take up any significant percentage of it, so perhaps I'm unable to see it from her point of view, but I don't think that showing me things I like, that I might otherwise have missed, is a 'problem' that needs to be 'fixed'.
Again, just my opinion. Can I ask what other social networks your mom has used, and how she found those, in comparison?