Can putting flea medicine on a dog more then once in a few days hurt the dog?

I put flea medicine on my dog a few days ago and then today she got covered in crap and got a bath, then not knowing that I put some on a few days ago and thinking that the dog was clean now an needed the medicine my grandma put more on her. Would the bath cancel the first dose out or is it a problem it is a cheapish kind of flea meds I dont know if that makes a difference