My friend isn't acting like herself?

My friend hasn't been acting like herself recently. She was diagnosed with depression about 6 months ago. But for the past month, she's been this happy, upbeat and positive person. She's actually the most positive person I know now. But these past couple days, she hasn't been acting like herself. Her phone signatures are always depressing like, "Iwanago2eternity" or "blad+blood".. and she always use to write stuff like "!hi!!" or " whats up?? :DDD" and now shes just like "hey." im worried about her i dont want her to go through depression again. whats goin on with her?