Fellow passenger, MaggieGremminger, who also witnessed the incident, said she was "disgusted and traumatized" by the incident.
Lara said passengers could hear the dog's "cries" throughout the flight.
"They assured the safety of the family's pet so wearily, the mother agreed", Lara wrote.
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. The dog had died.
"This was a tragic accident that should never have occurred, as pets should never be placed in the overhead bin".
Gremminger told People once the dog was found dead, the flight attendant became "frazzled" and insisted she did not know there was a live animal in the carrier.
"I want to help this woman and her daughter", she tweeted.
United Airlines issued an apology to the passenger saying the dog should have never been placed in the bin and quote "we assume full responsibility for this tragedy". "The woman, crying in the airplane aisle on the floor", Gremminger said. "We are thoroughly investigating what occurred to prevent this from ever happening again". The airline charges $125 each way for in-cabin pets.
According to the airline's website, pets are allowed on most flights within the U.S. In-cabin pets must travel in approved kennels that can fit completely under the seat, where the kennel must remain at all times. Proponents of animal-friendly flights have long argued that sending crated animals into the baggage compartment-where bigger animals typically ride-for long flights is inhumane and cruel; scores of animals die each year while in the baggage compartment, the Department of Transportation reported.