And that's vol 1 till we get vol 2, thanks for reading!
Now, I haven't seen any more of vol 2 than you have, but my suspicion is:
That guy in the fox mask who gave her the natto is one of the few remaining humans (they're in hiding) and it included some stuff to trigger her transformation because the humans still know how to do it?
Oops: The version that was up for 3 hours was missing page 21 - there's no big plot stuff in there, but some nice art, so if you want to see it that's fixed. Sorry!