My my, what a surprise... not.
Now the interesting thing is that the witch is obviously Elsa from the future, but what will happen to present Elvie? As the past is already set for what happened between Elsa and Elvie, present Elvie will likely not interact with past Elsa, but will she simply come back to this moment after whatever she did in the past and be like "oh hey Elsa, I know I look older than when you saw me earlier today, but that's totally normal, don't worry"?