I am watching all health posts for any signs of SDA virus and that big round lump in the middle of her throat is classic. Now I start the questions
Have you brought in any new rats recently? Have you handled strange rats then gone home and handled your own within 3-4 hours after? Have you been to the vets in the last week or so, petstore, etc?
Just in case I will give you more info on if it is SDA Virus (very contagious rat coronavirus)...do you have other rats at home?
I will post a pic of Clare's the largest I had seen before. Usually they are smaller
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Watch her eyes for any facial swelling, connective tissue in the front of the eye being visible
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Also hold her sides to your ears and listen to her breathing. SDA doesn't always give them noisy breathing but constricted where the lungs aren't getting enough air.
I'll wait to hear what your answers are...