I treat them as a masterwork Heal tool (so +2 to the check) but only in regards to diseases. Even if the book doesn't identify the disease per se it is invaluable in treating symptoms.
quote:
To treat a disease means to tend to a single diseased character. Every time the diseased character makes a saving throw against disease effects, you make a Heal check. If your Heal check exceeds the DC of the disease, the character receives a +4 competence bonus on his saving throw against the disease.
So if you give her the antiplague along with whatever remedies you and the cleric can provide it stacks all together.
+2 for the books, +5 for the antiplague, +4 for the successful heal check = 11.
I will also let you make a DC 15 heal check to give the girl a physical so you can better gauge how much damage has been done and how far she has to go.