I have always fed our hammy right up for the same reason! Yes I think raisins are considered a bit sweet - but if your dwarf hammy doesn't have diabetes at present then 1 raisin a week should be fine
I give our Syrian 1 raisin a week. I'm not sure about potatoes to be honest. On some lists it says potatoes aren't good for them but I think a tiny bit now and then is ok. Boiled rice is definitely ok. In fact our hammy cleaned the dish quickly when I put some out the other night. I put two "extras" out each night, as well as his hamster mix and piece of veg. Usually out of: Pecan nut, brazil nut, walnut, cheese, raisin, fresh coconut, a hamster treat, a piece of dandelion root (Zooplus sell bags of them).
Actually a dandelion root might be a good thing for her as well - it's a natural detox type thing and is also wood to chew on. So it should help any flagging organs
Sounds like the main thing is have her cage in a draught-free place and have the room temperature 20 degrees all the time.