I would say, from what Nancy says, there are a couple of options. You could either take the wheel out for 3 to 5 days and let her run in the exercise ball each evening. But - I seem to remember you had some issues with the ball (falling apart or something). Also I think this would stress her a bit having her wheel taken away.
The other option is change the wheel. Although this means spending money it is probably worth it and on top of that you would have a quiet wheel
. I have a question though. How big is Scarlet - approximate length - and do you know what she weighs? If she is particularly large then that would help decide a) if it is the wheel and b) which wheel to replace it with. For example Charlie is quite a big Syrian and I thought some of the wheels like the Wodent wheel, might cause rubbing on the side as they are only 7cm deep and he is big. He was also a bit long for the 27cm wodent wheel so I got him the bigger 30cm Wobust wheel - which is really deep - overkill really - but there is no way he can rub his sides in that and he can run with a straight back. He loves it.
It's difficult making these decisions when they involve money. There are plenty of people use comfort wheels with no issue, but if you have a large Syrian or she just happens to run funny, it could be to do with the wheel.
If you had a vet check you could rule out mites and the vet would give an idea of what other causes it might be. This would also cost money but might save on buying another wheel if it proves unnnecessary. If it is that she needs a bigger deeper wheel, the Wobust wheel probably wouldn't fit in your cage (or if it did it would take up an awful lot of the cage!).
A vet check would tell you what is what but I know you are concerned about the cost.
There's another thread I found with a similar issue, so I've linked it. Fur loss can be mites, or bedding allergy, or hormones, or old age. If she had mites she'd probably be scratching a lot. You've already changed her bedding (not sure what you are using now, sorry, but they can be allergic to any type of wood bedding, or hemp but paper bedding or Carefresh is hypoallergenic I think). If she had an allergy she'd probably be scratching too and possibly have other symptoms.
That leaves old age, hormones, over grooming scent glands, rubbing on the wheel or some illness. If she seems well and is eating and drinking ok, maybe just observe her for now and not worry too much. Do you know how old she is?
I wouldn't want to say try another wheel without knowing more, personally. Unless you have the cash and want a better wheel! But if you want to ask someone to get you one for Christmas I'd say either the 27cm Wodent Wheel or the California Storm wheel would be good. Both good wheels and quiet. Depending on how big she is - the california wheel has a running track of 10.5cm diameter, the Wodent is 11cm but not so deep. Height might be an issue in the cage. As long as your cage has an internal height of more than 32cm the 27cm wodent wheel would fit. The California Storm wheel has adjustable height but the lowest setting is 11.5 inches, which is just under 30cm.
Here's the link to them
The Carolina Storm Wheel - * * * * * * * * Carolina Storm Hedgehogs
Here's the other link
Bald patch