PLEASE HELP!!! REALLY GROSS!?

my puppy honey is a Chihuahua / Terrier and she is 7 months old and recently i came home from school and she was eating poop from my backyard. ewww!!! right gross ik!! i also have another dog hope, she is a 2 year old maltese so i have to feed them separately in the morning because of the adult and puppy food issue but when i leave around 6:40 am and when i get back at 4:45 pm then i feed them again so they dont have any food for that time until i get home... i do give them enough food to in the morning to last them till i get home and they also they have lots of water for the day when im gone so just curious is it a good ideal to leave the food out for them because they r both enclosed in the same pin that leads to outside in my backyard and they r both different ages so they have different food and i dont know if its ok for them to share the food because of their age differences... so how do i get the puppy to stop eat poop??? i just caught her a couple weeks ago and just an hour ago doing it. its rlly nasty so how do i get her to stop....? and why is she doing it??? oh also my backyard is neat and i try to clean the poop every other day and sanitize the area with simple green. please help me with this!! plus ive herd that dos eating poop can give them parvo and them they die so how am i suppose to train her to not eat it ? thank u