"Tonight I was on a plane where I witnessed a @united flight attendant instruct a passenger to place her dog carrier (with dog) in the overhead compartment. The passenger adamantly refused but the flight attendant went on with instruction," Gremminger said on her Facebook page.
"At the end of the flight - the dog was found in the carrier. I am heartbroken right now. I didn't question the flight attendant, but I could have. I assumed there must be ventilation as surely the flight attendant wouldn't have instructed this otherwise. I heard the dog barking a little and we didn't realize it was barking a cry for help."
Gremminger said that the passenger was adamant about not putting her dog in the overhead bin, but the flight attendant continued to ask the passenger to put the dog in the carrier and place it in the cargo hold.
"By the end of the flight, the dog was dead. The woman, crying in the airplane aisle on the floor," Gremminger said.
In a statement to Busines Insider, United Airlines apologized and took responsibility for the incident:
"This was a tragic accident that should never have occurred, as pets should never be placed in the overhead bin. We assume full responsibility for this tragedy and express our deepest condolences to the family and are committed to supporting them. We are thoroughly investigating what occurred to prevent this from ever happening again."
However, the airline declined to comment on its official in-cabin pet stowage policy and whether the passengers have been compensated for their loss.
Michael Hohl and Amber Maxwell had boarded their flight when they noticed a passenger napping across the row they were supposed to be sitting in.
Instead of waking up the snoozing man, the pair decided to sit a few rows in front of their assigned seats.
Hohl said that after he and Maxwell sat down, a flight attendant asked if they were in their assigned seats. When the couple said no and explained why they had moved, Hohl said the attendant declined their request for an upgrade and asked them to return to their original seats.
Hohl said that although he and Maxwell did as they were told, a U.S. Marshall later boarded the flight and asked them to get off the plane.
6. United Airlines CEO's heart transplant comes under scrutiny
Following United Airlines CEO Oscar Munoz's apology over Flight 3411, people began questioning whether his wealth played a role in the heart transplant he received last year.
Munoz had a heart attack on October 15, 2015, one month after he took over as United's new CEO.
Less than three months later, he received a new organ.
Since the waiting list for a new heart was reportedly up to 4,200 people at the time, questions have risen about how he was able to get a new heart without waiting very long.
7. Dad accused of trafficking his own daughter on United plane
The wife of a Mexican man who was accused of trafficking his own 3-year-old daughter on a United Airlines flight spoke out about the incident on April 17.
Maura Furfey, a Spanish teacher and mother of three, says that her husband and daughter were returning from a trip to Mexico to visit her husband's mother and great-grandmother, "who they see but once a year."
Apparently another passenger, who Furfey says was "obviously inebriated," expressed concern to an airline employee that the fair-skinned child didn't look like her Mexican father, raising suspicion that he had kidnapped her.
The mother of three says she burst into tears when she learned the details of what her family had gone through.
8. United Airlines stock plummets $800 million amid controversy
United Continental lost about $800 million in total value the day after the video of Dr. Dao being dragged off Flight 3411 became a major news story.
Shares in the company declined about 3.8 percent in mid-morning trading, a steep drop for a major company like United.
9. Woman claims United Airlines employee forced her to back of plane in tears without explanation
A New York woman filed a $150,000 lawsuit against United Airlines, claiming she was forced from her business class seat to the back of the plane by an employee without any explanation during a flight last year.
Karen Shiboleth, a 24-year-old Columbia graduate, was traveling to London to attend a master's degree program at Kings College on September 10, 2016.
Shiboleth claims that ten minutes prior to take off, a United employee boarded the craft and demanded she vacate her seat in United BusinessFirst and move to the back of the plane.
The lawsuit alleges that nobody would explain to Shiboleth why she was being moved, and that when she expressed her confusion, the employee took her arm "without consent" and forced her to a middle seat in the back of the plane.
To make matters worse, the unidentified worker reportedly called her a "c--t" during the interaction, bringing Shiboleth to tears.
10. Professional golfer claims his clubs were snapped on United Airlines flight
An Australian professional golfer took to Twitter on April 24, claiming his golf clubs were destroyed during a recent United Airlines flight.
Veteran golf pro Matthew Goggin said he opened his checked bag after his trip, only to discover that his precious clubs were snapped in two.
"First time in 20+ years I've opened my bag to find this..." he wrote. "I was going to complain but I must admit I'm a little intimidated by United."
11. Giant rabbit mysteriously dies aboard United Airlines flight
Simon, a 35-inch behemoth, was traveling from London's Heathrow to Chicago's O'Hare to meet his new "celebrity owner" when he mysteriously died in the airline's care.
Annette Edwards, Simon's breeder, says that both she and Simon's buyer are extremely upset and confused by the incident.
"Simon had a vet's check-up three hours before the flight and was fit as a fiddle," Edwards said. "Something very strange has happened and I want to know what. I've sent rabbits all around the world and nothing like this has happened before."
Simon was the son of the world's current largest rabbit, Darius, who is a whopping 51 inches long.
The 10-month-old rabbit was reportedly on track to out grow his father and eventually steal his title.