Could need antibiotics.Bartonnella can cause this.It's a 40 dollar blood test(here anyway).but it takes 1 week to find out.Zithromax or Azythromycin gets rid of bartonnella and the worst upper resporatory sicknessess.Or she could need predisone because she may have broncitis.But she would need an xray for that.
I know you said it was in her throat but she may have broncitis so bad it made her throat red.
I'm leaning more toward bartonnella.
Then there is Chlamydia but that is WAY to expensive to test for.It cost us 900 bucks to find out my cat Trudy had it VERY bad.But she had wet coughs and laringitis and snotty nose.
I doubt your cat has that.
I'm no expert.But throwing things out to ask your vet.
she needs a vet for sure.
I hope she gets better quick.Good Luck and I'll say prayers.