Did the vet listen to her breathing using a stethoscope?
Have you changed anything in the cage (liter, etc) or in the house? Could just be porphyfin.
It does sound like porphyrin. Porphyrin looks just like blood but is actually a fluid secreted by the Harderian gland which is located behind a rat’s eyes. If porphyrin is present it usually means the rat is stressed and/or sick. Besides around the eyes, porphyrin can also appear around rats' nostrils.
You can call your vet and let her know you're now seeing porphyrin and see what she says.
Are you hearing any respiratory symptoms? Do you hear any sounds when your rat is breathing? Rats' breathing should be silent. If you're hearing any sounds your rat could've developed respiratory disease after seeing your vet.
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