Diana Ramos, a 66-year-old Las Vegas resident, was found unresponsive by housekeepers in a room in the hotel near Philadelphia airport on Monday evening.
She was pronounced dead at 10.40pm by medics, officials told The Independent.
She is believed to have been on a layover in Philadelphia after finishing her shift on a flight from Los Angeles when she died.
She was meant to check out of the Marriott two days before she was found dead, reported ABC6.
Her mysterious death is now being treated as suspicious though there were no apparent signs of forced entry into the hotel room and no signs of a struggle.
No weapons have been found near her body.
Philadelphia Police Chief Inspector Scott Small said that the flight attendant seemed to have suffered a “sudden death” and that she was “on several medications” at the time, with sealed prescription bottles found in her room.
No arrests have been made and autopsy results have not yet been released.
“Everybody is still trying to figure out what happened and why her crew just left her,” an anonymous American Airlines flight attendant told People.
“A lot of moving parts and questions right now. Very sad.”
Another unidentified flight attendant told Fox News that they spoke to Ms Ramos’ flight crew, who said she was supposed to work as the lead flight attendant back to Los Angeles.
“The crew is saying they were staying at a hotel located inside of the Philadelphia airport,” said the flight attendant.
“They didn’t meet in the lobby for pickup as they normally would due to the hotel being located in the airport. No van shuttle being needed.
“Upon reaching their gate and realising that one of the flight attendants wasn’t at the gate, the crew notified the gate agents they were missing a crew member and one of the crew members [said] that as far as they know, another crew member tried to call the hotel twice to get them to check on the missing crew member.”
American Airlines released a statement saying that its staff “are devastated by this news”.
“Our thoughts are with the family and colleagues, and we’re doing everything we can to ensure all affected have the support they need during this difficult time,” the spokesperson said.
“We will continue to cooperate fully with local law enforcement in their investigation.”
A spokesperson for Marriott said that the company is cooperating with the Philadelphia Police Department and directed further questions to it.
The Independent has reached out to Marriott and American Airlines for more details.