DO NOT USE SENTRY NATURAL DEFENSE FLEA DROPS FOR CATS!
These drops have only "natural" ingredients like peppermint oil, clove oil, etc. My roommate put some on her cat, between the shoulders as directed. It is very smelly and the cat freaked out. Later she vomited in both our bedrooms so we washed it off as best we could. She's been drinking and eating very little and is very lethargic. I started looking up reviews on places like Amazon and found that lots of people have had problems. A few cats have died!
There are some complaints for the dog version as well, but mostly that it's ineffective and causes hair loss.
2. Peppermint oil is not recommended for use anywhere near cats.
If ingested, the peppermint plant and its oil could indeed potentially cause harm to your cat. Cats are especially sensitive to peppermint oil, and effects such as gastrointestinal upset, central nervous system depression and even liver damage could occur if ingested in significant quantities. Some peppermint oil formulations also contain aspirin derivatives, which could result in additional toxicity. Furthermore, if inhalation of the volatile oil were to occur, aspiration pneumonia may be possible. Based on this, we would not recommend using peppermint leaves or oil in areas where your cat is allowed access.
It sounds like your cat has the classic symptoms. I realize that it was not "ingested", but absorption would have the same results, I would think. I hope that everything is ok. I would continue to wash that area for a while, since oils are hard to remove, especially the skin where it would be absorbed. If possible, get water into her to flush out whatever may be in her system. And good luck.