Employees heard "strange noises" coming from the machine when they realised she was missing.
But it's still not clear what caused the accident at the Economy Locker Storage Company in Muncy.
The 35-year-old had been standing on a set of stairs on wheels before the accident, according to coroner Charles Kiessling.
For two hours Raper's legs were trapped in the machine before he was freed, He died the next day from his injuries.
Witnesses said firefighters spent about 45 minutes disassembling the large machine in an effort to recover the woman's remains.
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However, because no one witnessed the accident, Kiessling said it's unclear how she may have ended up in the grinder.
"We don't know if she fell in or was pulled in as she was perhaps reaching for something in the grinder, which was about six feet off the ground", he told Williamsport Sun-Gazette.
The Occupation Health and Safety Administration opened an investigation into her death.
Greninger was described by friends as "an awesome person" who "touched so many lives". This is the first reported death at the facility.
Her neighbour said: "My heart goes out to everyone who is affected by this".