This girl on facebook has tons of followers, what's up with that?

[Nick]

So I've been chatting with this small group of interesting individuals over the holidays on Xbox Live, and as always, I add those I like after talking for a while. I'm going back to Uni soon, and I don't bring my Xbox with me, so I like to add those I like most, to facebook.

This girl has her profile set to private, so she had to msg me first, before I could see her profile. There is no "add friend" option, only a "follow" option. She has over 19,400 followers and some of her posts have like 400-500 likes.

My question is, why/how is it that I cannot add her to my friends list, and how can someone have so many followers? I know like bots exist, but do they follow you and like your stuff?

I feel slightly paranoid now, it just seems odd to me.
Thank you for your answers!

[Janet White]

She's a public figure or a fan page. (Not a normal user account.)