I'm not really sure what "croupy" means ^^ But Pixel saw the vet today and it's an upper respiratory infection- which is why the antibiotics she was on before (for what I think the vet thought was kennel cough- she only heard symptoms over the phone) didn't do much. She'll apparently get over it over the next week or so, probably. Apparently it's just going around our local shelter, which is where we got her.
The vet suggested benedryl if we feel she's particularly stressed (although she didn't specify how much...), but other than that it just needs to run its course.
Thanks for the help though!