@Waitingbee57: Thank you for doing research before buying her! Its such an uncommon practice unfortunantly. 🙁
Its certainly possible she was sick before purchasing her, though Petco/Petsmart is required to place all new isolation for a few days. At Petsmart, we placed all small animals in isolation for at least 3 days. This isolation period in conjunction with the 3 weeks to develop symptoms leads to me wonder if it weren’t a “hidden” case of wet tail where the symptoms are not as pronounced as they are in other hamsters.
The first day you noticed her refusing to wake up gives me that indication, because this was the most tell-tale initial sign that one of our Syrians had wet tail. We would usually notice light diarreah on the bottom, but it was rarely as “wet” as pictures showed. Even if the feces were soft, in conjunction with the extreme lethargy we would always remove and treat for wet tail. Did you observe any softer fecal matter in the cage? Was her rear even the slightest bit tainted? The other reason I wonder if it might have been a less pronounced version of wet tail is because of the time frame. If the hamster passed within months of purchasing, I would be stumped as all heck. However, 3 weeks isn’t completely implausible. A bit unusual, but nothing I haven’t seen in the store before.
Its great that you chose to use paper bedding! That certainly helps a ton with all small rodents.
Although this very likely had nothing to do with the hamster’s death, if you do decide to add another hamster to your family in the future, I would return that cage. It is far too small for a Syrian (even if you were to add a second cage, it would still be too small) and is actually too small for dwarf hamsters as well. I hate how the pet stores sell them. Hamsters need at least 360 square inches of floor space to run, and I always recommended more than 400 square inches of floor space for the Syrians I would sell. While working at Petsmart, I begged my customers to NOT buy these cages, as they are 1) far too small 2) dangerous (did you ever notice your hamster bite at the bars? Not all do, but those who do are at risk of fracturing their teeth) 3) very easy for hamsters to escape from. It hurt sales, but I had the fewest returns/deaths on live animals than anyone in the department. Its off topic, but if another hammy is in your future, I would get your money back for the cage and run to Home Depot or Wal-Mart. Purchase one of those large, plastic, transparent Rubbermaid bins and create a ‘bin cage’. If you want a prettier plastic one, I would try and find one online. There was only one plastic cage we ever sold that was suitable for dwarves, but I’ve yet to see any cage sold in major retailers that is suitable for Syrians.
The Forti-diet isn’t bad, so that definitely didn’t do anything harmful to your little girl, and I know exactly which seed mix she recommended, which also isn’t bad either. We use to feed this exact diet to all of our hamsters. It isn’t terrible for Syrians, but definitely AVOID if you ever decide to get a dwarf hamster. It probably wasn’t anything diet wise which is good. (Again, if you decide to get another hamster in the future, I have been using (and recommending) Supreme Hazel Hamster OR Oxbow Hamster Food. My hamster loves it.)
I know I kinda went on a tangent, but I’m very curious as to whether this was a more quiet case of wet tail. The symptoms you describe and timing lead me to wonder. Being cold too was another thing we noticed at work in the late stages of wet tail; for the vet to suggest hibernation is very, very bizarre. Hamsters usually don’t hibernate unless the house is 50 degrees F or less. If you haven’t yet cleaned out the cage yet, maybe look through all tunnels and bedding to see if any stool appears loose?
I wish I was of more help, but I am very sorry for your loss, and I would at least call Petco to see what they can do. If you still fall under their “pet insurance” window I would absolutely return the animal and get my money back.