What should I do about this old friend?

[Mrs. Carey Price]

So I used to be best friends with this girl. And last year she got a boyfriend and so did I. We kinda just stopped talking, and I don't know what happened. It was depressing. But that was over a year ago. So basically, I just got engaged on December 15th. And just today I noticed I got a message from this former friend on facebook. The message was sent to me on Christmas saying congratulations and saying she didn't know why we stopped talking. Well, for some reason I never got a notification for this message and didn't even know it was there, Well I guess she figured I was ignoring her and got mad/upset and blocked me on facebook. Should I text her hoping she still has the same number and tell her what happened? Or should I just leave it alone forever?