Just a thought, does she get on well with either of your other kitties. If she does maybe you can take two of them to the vets to keep each other company.
I always take Bramble & Tigs ( in the same carrycase) to the vets together. As if I take one, they cry all the way, Bramble will try and grab my arm as I change gear... good fun while driving !!! But when they are together they are quiet.
All the best.. Hoping it goes better than you expect.
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