Somewhere I heard that only male dwarfs can be housed together.... I remember a friend telling me about how she had two dwarf hamster girlies, both from the same litter and grew up together, but they eventually got into fights. She said that one of the girls chewed off the other dwarf's ear and foot.
To be on the safe side, I think she might just want to go with a single hamster. My dwarf boy has lived with us, by himself since december of last year. He still seems happy and fine without a cagemate.