She "deleted and blocked" you? I don't like being rude, but, if you've got the sort of friendship that can be ended over the internet then the first thing you ought to do is take this as a lesson. Even with friends you know in real life, the way that people talk over the internet is so different from real life communication that It absolutely has to be regarded differently. If the bulk of your communication occurs online, and if you've got a friendship that can be ended with the click of a button, you should keep these frailties in mind, regarding the relationship with the same distance as the medium through which you communicate suggests. Point being, while there are absolutely exceptions, relationships that are primarily developed and maintained over the internet are rarely as mature or strong as the relationships we develop in person.
Second, if you've got a friend who, when she does something wrong, instead of owning up to what she's done runs away from confrontation, this does not suggest that she's a very mature person to start with. If you've got a secret that has to be kept, well, first off, as you're probably already aware, you shouldn't share it to begin with... but if you do share it, then make sure that the person with whom you share it is mature enough to handle the responsibility of the secret you share.
And finally, you're going to have to be ready to accept the responsibility for your own actions. And trust me when I say this, I know how much that sucks. I've eaten so many of my own words I feel sick sometimes, but part of growing up is learning to face up to your mistakes, and not just that, but to own them. Jeff Garlin once said that when you act like a jerk, if you're going to apologize then you can not make excuses. But, of course, this doesn't just apply to when you act like a jerk, it applies to any mistake that one can make. In this case, a secret was told to someone who, in retrospect, it should not have been told to. Now the consequences of that action have to be lived up to, and depending on the nature of the secret, living up to those consequences could suck big time. But part of life is understanding that thing's aren't always going to be sunshine and lollypops. It'll get bad, but with time it'll get better. Just do your best to deal with the ramifications of the situation, own up to any mistakes you made, and face whatever happens head on.
As for your friend, one of those other unfortunate facts of life, is that there is nothing you can do. People are going to make bad decisions from time to time, some more often than others. Your friend made a bad decision in betraying your trust. But like it or not, you can't change her bad decision, and you can't change her. Really, you've only got two options. You can stay mad, or you can forgive her. I don't think I need to go into too much detail about how forgiving her is the more mature option (as well as being more psychologically healthy), and that if you do forgive her then you've got to really forgive her, there's no going half way and holding the incident as a weapon for the future. That said, even if you do forgive her, also be sure that if you ever do decide to tell her a secret again, you make sure that she's grown up enough to handle it before you do.
