Here is the
MSDS for Mod Podge.
MSDS, for those who don't know, stands for Material Safety Data Sheet, and is a document that contains information about chemical substances; i.e. possible toxicity, how to handle it, first aid, etc.
Nutshell: Mod Podge is made from "residual vinyl acetate" and the vapors can cause respiratory irritation. First aid for the symptoms is to get fresh air. If symptoms don't subside, seek medical attention.
There are several different Mod Podge products. I'm wondering if somehow you used something other than what the author used. I'd email and ask what her experience was like.