Alkaline Phosphatase is an enzyme found in the blood and produced by the liver and bones. It indicates liver disease (or damage) as well as bile duct problems and calcium problems, but mainly as liver function indicator.
Zilla's results were normal indicating she had no problems with her liver.
In FIP, I have observed that some cats do have liver involvement, usually in the form of hepatic lipidosis from the sudden weight loss sometimes seen in the disease. It is also usually accompanied by the symptom of jaundice which in a cat can be easily seen on the inside of their ears, gums inside their mouths and can sometimes be seen also on the inner side of thier lower eyelids. You will also frequently notice darkened urine with jaundice in FIP cats.