I would recommend Mylicon for infants and these 1ml oral syringes.

Draw up 0.1 and give once to twice a day. This will relieve gas symptoms. I wouldn't recommend it regularly on younger ferrets as it can cause a need for the medicine over time. This is because their digestive tract will be used to needing the meds to pass gas. But in an older ferret with gas trouble, daily use is fine.

I wouldn't recommend recovery milk for ferrets. The milk will cause MORE gas in your ferret. Have you considered Uncle Jim's Duk soup? This will help give the extra calories to your girl without upsetting her tummy.

Have you asked the vet about Sucralfate? It can help ferrets with upset tummies. It's a 1gram tab that is generally mixed with 10oz of water. Then the ferret gets 0.5ml to 1.0ml twice a day.

Has your vet checked her blood glucose and felt for any masses? If you ever need a new vet try http://ferret.vet for a vet.