Hello, my name is***** and I have over 20 years experience as a veterinarian. I am sorry to hear that your kitty had Dog Vectra applied. The concern with that is that Dog Vectra contains Permethrin which is a pyrethrin insecticide that is highly toxic for cats.
While I am pleased to hear that you were able to bathe her, you need to bathe her fully in tepid water and a degreasing agent such as Dawn dishwashing detergent until the spot where Vectra was applied is no longer greasy.
Do not vigorously rub the area, as that will increase absorption. But do gently bathe that area to remove as much as possible. The less she absorbs the better. If you can still see where the medication was applied concentrate on getting that area clean. You may need to bathe her several times.
With a pyrethrin based product common symptoms of this toxicity are drooling, nausea, diarrhea, dilated pupils, tremors, incoordination and in very severe cases seizures.
The problem with this toxin is if they cannot eat and drink they get very dehydrated and worsen quickly.
If the tremors are very bad they can cause an increase in body temperature and muscle toxins which can cause brain damage and kidney failure.
So if their body temperature rises and they are tremoring consistently we put them on fluids to bring down the body temperature and flush out the muscle toxins.
If actual seizures occur she will need intravenous medication for that.
At home all that can be done is decontamination (bathing) and nursing care.
That includes keeping her indoors, quiet and away from stairs so she doesn't fall and hurt herself, and helping her eat and drink. Keep an eye on body temperature (concern is a rectal temperature more than 104F). Keep her in a quiet area as the more she is stimulated the more she will tremor or seizure.
If she seizures she must be seen by a veterinarian. There is nothing that you can do at home for that.
As far as how long her symptoms will last, that will depend upon whether we can get most of this off or not.
Usually symptoms last 2 to 3 days if we can get most of the product off.
If this is an extreme exposure then symptoms can last a couple weeks.
Very rarely there is long term damage.
In many cases if we can remove most of the product before it is systemically absorbed they do very well.
Please let me know if you have any further questions.