"Have you ever done anything of this magnitude before?" you ask her.
"No, never. But I have to try, don't I?"
If she feels she has to try, she has to try. Even if it goes wrong somehow, you can't see her making the situation any worse than it already is. An earth pony, Cherry, also steps forward and volunteers her plan: to take anypony who wants to go away with her, in the Twinkling Balloon, before the dome is erected, in case areas of Equestria that are not Ponyville are being targeted by fewer meteors and thus safer.
This is what Rarity was hoping for, isn't it? Ponies besides yourselves stepping up to defend their homes? It's beautiful.