Welcome to Ask The Doctor.
There is no pint in waiting for the fever to come down. You should see a doctor now, as very high fever at such age are most commonly due to viral.
You can do cold sponging of your child and give Paracetamol Suspension to bring the fever down. But since she is just 4 months old, a doctor's evaluation is must to rule out any infection and requirement of antibiotics.
Just check if she is breathing fast, if her respiratory rate is high then she would require to see a doctor and evaluation for Pneumonia.
I hope it helps.
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