Sounds like no changes prior to the onset of her condition.
I would think a cage change would stress her out - in another thread you said she is an older hamster so she, like humans, will be unsettled by change, which won't aid in her recovery.
As she has obviously seen a vet already it appears that there are no obvious causes (i.e. mites), and her diet is the best it can be given her present eating habits, so it may be an allergy. I haven't experienced it with Megazorb but it might be worth trying an alternative.
I'm sorry to hear about her condition, it sounds really uncomfortable for her and distressing for you too.