Dog Flea Medicine on Cat--help!!?

well basically my sister bought kitten flea medicine on ebay but when we got it, it was dog flea medicine with instructions on how much to use on her. We looked it up on yahoo answers and the internet and we're running low on money so we just used it. My cat started to scratch more and shed within the hour so... show more well basically my sister bought kitten flea medicine on ebay but when we got it, it was dog flea medicine with instructions on how much to use on her. We looked it up on yahoo answers and the internet and we're running low on money so we just used it. My cat started to scratch more and shed within the hour so we washed it off. (i think) I went to the vet and they said that it could be eating her flesh (it's been on her for more than a week and she's fine) but they said i should just get a $50 check up. Most of my friends are telling me to just get her kitten flea medicine and put it on her. Please keep in mind, that I'm not the richest person in the world and i'm going through money problems right now so $50 isn't that easy for me to get.
Update: i used frontline plus :)
Update 2: also there's another problem, my house is now infested with fleas.
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