This is punctuated correctly.
"Marshmallows are my favorite snack" is a complete sentence unto itself.
The comma instead of a period shows that the sentence spoken is part of the whole sentence, which includes the speaker (she) and a word to describe how the speaker said it (explained).
Inclusion of only the most important detail
"The grass is always greener on the other side," she chirped, but her advice meaned nothing to me. I hope I helped :)
Answer:
I wonder what would have happened of they didnt see the burning church? I haven't read the book in a while lol