What does her breathing sound like? If it's a URI you do need to act quickly. One of my rats had a URI a few months ago, and we ended up bringing her to the emergency clinic because we were so worried. She seemed fine in the morning, but by the time we left to take her we were afraid she wouldn't make it through the night. It progressed pretty rapidly. Granted, she's fairly old - she'll be 4 soon - so rate of progression might be a bit different. Regardless, URIs can progress quickly, so I would highly suggest taking her to see a vet ASAP.