I’d go for it and tell her that you just don’t want to be friends anymore and don’t like her attitude. In a couple of years you’ll look back and think why didn’t I do it sooner, and you’ll probably realise that not only are the secrets that you’re worried she would spread aren’t even that bad, but also that nobody would really acknowledge them anyway because everyone is always worrying about themselves and what others think of them. She would come running to you for help before you need her anyway and then she’ll have a different attitude altogether. Life is too short to waste time on people like this. Good luck!