I can sympathize. My little Prima recently lost her sister, Donna to an unexpected heart problem. If she's young (I would say 6 months or younger), it's a risk, but you could try introducing her to a new animal. However, if they're still fighting terribly after a week, you'll have to separate them. With Prima, since she's over a year old & territorial, it wasn't an option. She resents the robos I even keep in another cage. She even fought with her sister so much after about 6 months that I had to get two cages that I kept next to each other (they would communicate & give each other kisses through the bars). Anyway, it basically depends mainly on the hamster's age, & if she's older, her personality. You'll want to get her a pal about her size, too, so if there are altercations, one won't bulldoze the other.