Hi Julie,
You're basically looking for a herb that interferes with the inflammatory mediators that promote serum amyloid secretion by the liver. The one plant I've found that does that is the Chinese herb Coptis. It can be added as a single herb. It's quite bitter, but if perhaps it can be disguised. Worst comes to worst, they can put it in gel caps - gel cap makers are available at many herb and supplement stores.
I'd give 1/8 to 1/4 tsp twice daily. It's a strong anti-inflammatory, too, so it may stabilize some of those other symptoms, too, including the itch, cystitis and colitis
Steve