Does Pheobe have any history of allergies or sensitivities? My Mr. Pigglesworth got a spot exactly like that unrelated to any topicals, and it was a booger to get rid of, since the more he scratched it, the more irritated it got, which meant he scratched it more. I wound up making him a rigid protective collar which he wore for a month; I can describe it to you if necessary.

Advantage and Frontline should not have any adverse reactions to each other and can be used alternately or sequentially with no problems.

Frontline is dosed for the size of the pet, not the density of the hair. A 10lb long-haired cat will use the same size as a 10lb shorthair, since it goes by the surface area of the skin, not the fur. You can wash all the fur, but the product lingers in the oil glands and remains effective, which is why it's billed as waterproof.

If it were my cat, I would wait a month and then apply a small amount of Frontline, purely to see if it is in fact a reaction. Irritation at the application site is one of the listed potential side-effects, or it may be simply a coincidental problem. If she is truly sensitive to it then you should see an irritated area regardless of the volume applied. I am both anal-retentive and intensely curious, and would feel compelled to know if my cat was having a reaction.

Also, if you are using it purely to control fleas and are not seeing any ticks, then you can use it every 2-3 months, instead of monthly, or switch to Advantage which does fleas but not ticks.

Or...you could get a prescription from your vet for Revolution, which blows all the others out of the water, IMHO. Love the stuff, and use it on all of mine.