Most of the time, they outgrow the poop eating...it's normal so don't get too upset..as far as letting her out on her own, I don't know how old or how big your puppy is, but, mine are never out in the yard by themselves(they're pee pad trained, but, when it's nice out, we go out with them for about 10 minutes and let them run(have a fenced in acre out back), but, never alone..there are hawks that fly around, and they can pick a little one up in a heartbeat..
When I catch Ginger grabbing a piece of poop, I clap my hands and say NO..she knows not to do it, but does it anyway..
As far as canned food, I have always given mine the hard kibble, I don't feel the canned is that great for them, they need the hard food..but, if your pup is having a hard time eating the hard food, maybe try softening it with some warm water until she's able to chew the harder..