The first thing she notices is that loud noise, followed by something smacking into her...And, that is sort of a smack, not really an impact. She has to wonder about that for a second.

But just a second, because the small-ish person that just ran into her is a lot more pressing.

"Oh! Sorry," and she'll extend a hand as well, see if she needs help. And feeling more than a little foolish for keeping her eyes on the storm instead of people that might be running around. "I should've been paying better attention. Are you okay?"

...And...M'gann can't help it. This is a very small Earth child from the looks of it. Smaller than Robin, possibly. It's hard not to be endeared, instantly.