09/20/2012 at 06:00 PM EDT
Maggie Rizer had done everything right, she thought.
The model had booked reservations for her two golden retrievers – 7-year-old Albert and 2-year-old Beatrice – on her flight from New York City to San Francisco through United Airlines's PetSafe program. She knew about the potential dangers of flying with pets, and though Bea had flown without issue in the past, Rizer did more extensive research to make sure she was doing all she could to protect her dogs from harm.
But when Rizer, 34, her husband, Alex Mehran, and their 10-month-old son Zander
landed in San Francisco on Sept. 3, they found out one of their family members had been lost along the way: Bea had died.
The golden retriever's passing was inexplicable. Bea was young and had undergone a requisite physical examination – and was found to be in perfect health – just days before the flight. Golden retrievers don't usually experience problems during air travel.
"We're completely devastated," Rizer tells PEOPLE. "[The airline] didn't even have an excuse."
In a passionate blog post
on Rizer's website, Bea Makes Three
, she paints a picture of United employees reluctant to admit wrongdoing or share any information about the company's internal investigation.
According to Rizer, her veterinarian performed a full necropsy and determined the cause of death to be heatstroke, "the absolute worst thing I could have imagined happening to her," Rizer says. "She died 30 feet below us, alone and scared. Nobody was there to help her because someone made a mistake."
In a statement, United tells PEOPLE that, "We understand that the loss of a beloved pet is difficult and express our condolences to Ms. Rizer and her family for their loss. After careful review, we found there were no mechanical operational issues with Bea's flight and also determined she was in a temperature-controlled environment for her entire journey. We would like [to] finalize the review but are unable until we receive a copy of the necropsy."
Rizer considered filing a lawsuit but hopes that speaking out about her experience will help inform people about the risks of traveling with a pet in cargo.
"I don't think dogs should be treated like bags," she says. "They're living, breathing creatures and parts of people's families." She adds that she will never fly with her dogs again.
"I'll miss her loving soul," Rizer says of Bea, who used to sit by little Zander and gently lick his face. "She was one of a kind. I've never had a dog like her. You can't replace a dog, especially one like that."
Though Bea won't ever be replaced, Rizer did adopt a rescue dog the day after Bea's death. "I have no idea what he is," she says of the mutt, named Jack. "You just have this hole and you try to fill it – and it's impossible to fill."