Can the vet give you something for the fur balls at all for Coco? Personally I find that fur balls make ours vomit but do not give the looseness you describe.
How about a really strict grooming regime to try and make sure that she does not swallow too much fur?
It might be wise to see the vet again though as diaorrhoea is not commonly caused by furballs. If the furball gets into the bowel it can cause a blockage or constipation but the looseness sound like she may have a bug or something that didn't get fixed by the first treatment.
I hope you get her settled soon so you can relax and prepare yourself for your operation. Wishing you all the best for that when the time comes