My family had a cat (16 years old) with dementia, hyperthyroidism and later cancer as well. What ended up calming her was Valium/Diazepam. First two where quite good to handle with meds and she ended up gaining weight and less vocal/yelling. Eventually she ended up having cancer and they decided it was ready to let her go. But in the mean time she had a good and even beter quality of live with the Valium.