Is my rat's stuffy nose a problem?

[nutsandberries]

My rat, Tumble, has had a stuffy nose for about a month now. She has excreted lots of porphyrin which i've wiped off with a wet cloth, and she's occasionally sneezing and shaking her body after sneezes. I waned to figure out whether this was something temporary I shouldn't worry about, something I can treat at home, or a reason to go to the vet.

I've been trying to nail down the possible causes and here's what I have so far. My rat that I had with her died about a month ago (we had to euthanize her due to pneumonia) and she's alone but she's not actually a very social rat so at least for the time being we're keeping her alone. This rules out communicable diseases unless symptoms of some of those take a while to show, but my other rat wasn't having any breathing issues at the time. There's quite a bit of fabric in her cage which I suppose could create dust, but it seems odd to me that it would given the breeder I got my rats from also had a lot of fabric in their cage. She could also be allergic to something, but she hasn't had a breathing issue before.

Thanks for any and all responses, I'm really grateful.