My bird has Pneumonia, and i dont know why?

Try adding more warmth bu placing a heating pad under the cage. Someone else suggested a heat lamp from the pet store which would also work. Just be sure it doesn't get too hot and make sure the bird can get out of the direct heat if it chooses. You will prob never know how/why your bird developed pneumonia, if you can't trace it back to another animal. Bacteria & fungus circulating in the air we all breath can lead to this illness in a susceptible bird. Don't blame yourself. You did the right thing by getting your pet to the vet for treatment. Hope she makes a full recovery, seems like she's getting good support fr you..