I’m no expert but I think it would help people if you know her length, age and maybe show a picture of her.
If she’s still very young I wouldn’t worry so much as she could be growing. Also, Ria is right, you get big and small hamsters. My previous hamster was tiny really and she fitted fine in a 21cm wheel with no arched back. I don’t know her length or weight as I’d never thought to do it before
My new hamster is massive in comparison, I had to get a 33cm wheel as her back was arching a lot, I know she’s seven inches long and weighs 200g. I’m not sure if she’s actually overweight though since pet shop bought hamsters tend to be within the hundred range. I’d adopted her but I guess she was pet shop. Breeder ones can be 200g so either mine is show ready or fat lol 😂
I think the general rule is for every inch they should weigh an ounce of course this is very general. Also I think you can tell looking at them like my new hamster does look ever so slightly on the podgy side so I reduce her fat intake.
The best picture I can find of each is them on the same wheel for comparison, small hamster was asleep so that’s why she’s like a ball 😂 it’s the best I’ve got, big hamster also I have upgraded to 33cm now so don’t think she’s tortured anymore!