This is Dr. David
you should be concerned.
she could have a septic joint infection in her knee
she needs to be brought to a hospital for blood cultures and blood test to check for infection in her blood stream and elevation of her WBC white blood cell count which I bet is elevated.
she most likely needs broad spectrum IV antibiotics
she needs a throat culture as well.
prior knee surgery and if she has foreign bodies in her knee from the surgery increase risks for infection at that site which can spread to the blood stream.
you should bring her to a hospital right away.
let me know if you have other questions.
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