Ok, this is before the translation, but I'm guessing at the last two panels, either Meiling gets REALLY concerned for Flan and/or Gensokyo and decides to keep a close watch on her, OR Sakuya just gave a strict direct order that made poor Meiling jump to action out of pure fear.
judging by Sakuya's expression in the fourth panel, I say she wasn't expecting to give Meiling orders and just told her why the gate blew on her. I go with your first option
Ah, well, the gate suddenly blew up for no apparent reason......I got engulfed in it.Off I go!That spiritedness is useless!No worries, I will put up a spirited pursuit,This'll be tough, but I'm counting on you now, Meiling.Yes, leave it to me.I will continue to watch over the young mistress* until the very end. Imouto-sama = little sisterBy the way, why do you appear so worn out?More importantly, look, now you've lost sight of the young mistress, haven't you?Just a-! Reverse, reverse! The young mistress went that way!Ah, yes!