I don't think that hamsters really get a fever? She just sounds like a normal aging hamster to me...if she was drinking a lot more than usual, eating less ect, then I would more likely suggest a vet trip, but two years is an old age for a hamster and as long as she is otherwise normal, I wouldn't say to worry. Sleeping more is definitely just the age, if she does get worse then maybe keep a close eye on her for other symptoms