It wasn’t clear it was her idea from the original post, but in that case I can see why you’d be perplexed as to why she didn’t show up. If you already felt like close friends before this (because some friendships can feel closer/more intense in a relatively short time) then I can see why you’d feel upset she suggested the call, then skipped out on it, only to be doing something else on Facebook at the time it was on.
If she hadn’t been on the site, you could more easily have put it down to something else coming up.
If you really feel a need to send anything, I would keep it to a brief “hey, what happened to you?” But really, it comes down to whether you’d like the friendship to continue anyway.