My kitten has cold and is not eating or drinking ?

I agree with eyJude take her to another Vet for a second opinion. Not eating or defecating is not good - something might blocking her e.g. string or something she ate. I think dark urine means low fluids or dehydration - try to give her some more water cats love freshwater or mix with tuna juice. Has she lost a lot of weight in a short amount of time? sounds pretty serious though.