Oh No!! The muzzle is extremely cruel. She is teething and MUST chew; it relieves pain and helps work the baby teeth out. It's what puppies do. Please please get rid of the muzzle. You have to manage the chewing, it's the only way she'll learn, in the long run. All puppies chew, I'd be very worried about one that didn't.
Likely she hasn't been abused, she's scared of you and for good reason. Puppies should NOT be "scolded" any more than you would scold a 6 month old baby for crying or pooping or whatever babies do. Why scold her? That's abuse for puppies, IMHO. She won't learn anything but to be afraid of you.
It's very common for puppies to eat poop. Don't punish her for it. Go out with her & pick it up immediately if possible. She'll grow out of it on her own.