I'm not on FB anymore, but have been thinking about going back. Anyway I totally get what Prairie Song is saying. At least I think I do. It makes total sense to me. Everyone uses FB differently and those who are the "super likers" need to get that some of us aren't as comfortable with that, and might even find it a bit intrusive. Anyway, I understand the need to clean up your account and unfriend those you really aren't in contact with and don't have much inclination to resume an online friendship. I don't think it's being mean, I think you're being practical and honest with yourself. I also used to pride myself that I had a small FB friends list (less than 100). I'm weird that way.
I think it's weird that she would contact you anyway. I'd probably get it that this person wasn't interested - or wanted a simpler FB account or whatever and I'd move on. If it was an online IRL friend then I'd be worried... but not someone I only see on FB and haven't been really friends with for years.