The Elmira Police Department said residents were out on a porch when they heard a "suspicious noise" and went to investigate.
Kayla Seals said she thought it was an animal at first, "I ran up and I see the little legs were dangling out the bag, so I said 'you guys, it's a baby.'"
Seals told CNN Affiliate WETM
she tore open the bag and saw the 8-month-old baby girl, "I picked her up. I took her in the bathroom. I mean, she was hardly breathing honey. Her eyes weren't even open."
"She wasn't breathing, but she opened her mouth for me and I dropped some water in there and she started gasping for air after I did that. Her eyes weren't opening so I cleaned her eyes, so eyes would open up to me and I just spoke to her 'c'mon baby, c'mon baby, c'mon sweetness,'" Seals said.
Elmira Police Sgt. Bill Solt said "the baby was dehydrated and currently in stable condition but expected to make a full recovery."
"We are looking about 72-hours in the bag," Solt said. "She's a miracle baby."
The infant's mother, 17-year old Harriette Hoyt of Sayre, Pennsylvania, has been charged with attempted murder.
"She is being charged as an adult, but is eligible for youthful offender status," Solt said.
"I can tell you she was with a friend of hers some distance from where the child had been left," said Chemung County District Attorney Weeden Wetmore. "It's a horrific case. It's incomprehensible how a young mother could leave her 8-month-old daughter in a plastic bag and abandon her."
Hoyt is being held in the Chemung County Jail. Chemung County Public Advocate John Brennan confirmed he will represent her at her next hearing on August 14.
Sayre's neighbors were shocked by the discovery, "All I want to do is cry for her. I could just feel her heart and what that little girl went through is wrong," Kayla Seals' sister, Karen Seals, said. "That little girl don't deserve that at all. All, everybody in this town, just pray for her."