You say that you usually put political notes, things about going to the store, straightforward updates, essentially. Not song lyrics.
Then you chose, in this case, to use a song lyric which could easily be a reference to suicide -- driving 100mph in the dark without steering would get you killed -- when, by your own admission, you don't usually use lyrics. Without attributing them as lyrics.
Then you get upset she posts "Yikes! Call me!"
Which is not something that poses the question 'what's up with her,' as you suggest, considering you originally thought she wanted you to call you because something was wrong with *her*. Or at least that's how I interpreted your 'Why, what's going on?'
Only after you replied in public did she explain her reasoning, which would imply you were willing to talk about her comment in public. Could she have made the second comment in IM? Yes. But you'd already replied in public, on your page, instead of taking the conversation to a private phone call like she suggested. You're blaming her for not divining your preference to move the conversation to a private place when you chose not to move the conversation to a private place after she suggested it.
How is that her being dramatic?
...or stuff like that. If you are depressed, you should be talking to a therapist, not updating Facebook.
Or maybe you should be reaching out to someone in any way that makes you feel comfortable, which is often half the battle for depressed persons. Therapy is all well and good, and sometimes incredibly helpful, but knowing someone not paid to care knows that you're having trouble right now and cares is worth that person's weight in gold.