[souffle]

I'm sorry to hear your hammy is poorly. I've never ever heard of a hamster suffering from this condition. What are the symptoms you took her to the vet for?
Fibreplex is normally used for rabbits and Emperid is not something I have ever seen prescribed for a hamster. Is the vet an exotic specialist?
I would be thinking that there is another cause for the weight loss. Things that often cause this are teeth problems thus not eating properly, kidney or liver problems or heart problems that are causing fluid to gather in the abdomen and this draws fluid out the bowels causing constipation. Lack of good bacteria in the gut can also affect them. If she is full of fibreplex she won't be eating normal food as she isn't hungry. Another cause can be a womb infection which does not show much except weight loss and sometimes a discharge. To try and help her gain weight you can try soaking her food and also giving a small amount of babyfood and porridge. Also plain chicken, egg white, cooked pasta, tofu (try one each day) and increase oil seeds like sunflower hearts.
I would maybe get another opinion and get teeth checked and tummy felt for lumps / bloating etc