my dog has a sore throat and stuffy sinus's?

I took her to the vet today and she got a shot it was dexamethasone 2 ml how long will it take this to start working? I hate my baby being sick. And what can I do to help her heal faster? Her little throat is red and inflamed and her nose is stuffy And she also has a cough.the vet said the shot last 3 days I want to comfort her so she gets better faster.. she has is cold/sinus infection but i hate seeing her not feel well...

You should have asked the vet who diagnosed, prescribed the medication and is legally allowed to prognose the condition the dog has.