When she got the antibiotics from the Vet did they do a culture? If not its possible the treatments she has gotten helped the condition but did not kill/cure the Bacteria/Virus that is causing the RI.
Bump your heat a bit in the mean time and get a culture done if you think she has come down again with one. (IMO)
I didn't end up getting a culture done because she didn't have enough symptoms to prove it was RI, only whistling. No mucus or any other signs, we checked her lungs as well.