i had a friend that owned a 2 hamsters and she took care of them really well. her hamsters died after well... 2 months. she was sad. they probably died because their bodies were tiny, but even though their bodies are tiny doesn't mean that they have to die that quick? right?!
it's possible the animals got sick right after she got them, but didn't recognize that they were ill. it's also possible that she had the bad luck to buy old hamsters, instead of ones just out of adolesence. Small animals like that generally have much shorter lifespans than dogs or cats. When I bought my pet rat in college, I knew they only lived 3-5 years, so I made sure to buy a baby rat that I could 'train' from being a ratling. Or youngster. or whatever. So that I could have her as a pet for as long as possible. Buying adult small animals, since its virtually impossible to know the age of said animal, is more of a risk.
Never trust a tall dwarf... he's lying about something.
Something no one here has touched on, also: Prey animals like mice, hamsters, and rabbits, tend to hide their illnesses. This is a survival instinct, because in the wild, a carnivore will look for the weakest, easiest kill it can find. Therefore, showing signs of sickness is very dangerous for small animals. She could be re-infecting the animals with a certain disease if the animals are kept in the same cage. Tell her to wash the cage thoroughly with a bleach solution, make sure no residues are on it, and get entirely new food dish, water bottle, bedding, toys, and so on. And to buy young animals. :)