It usually takes 24-48 hours before you will see a significant improvement after the antibiotics.
There are some tricks that you can use the help her feel better, though, while you wait for the anitbiotics to do their job.
You can put a pot of water on the stove on low or use a humidifier to add moisture to the air. You can also warm her food to stimulate the sense of smell. Many cats will not eat what they cannot smell so this helps to bring out the aroma. You can use pediatric (not adult) nasal saline in each nostril to help clear the mucus. And you can flush the eyes with saline to help keep them clear.
You should start to see improvement at any time, now.
Let me know if you need more help!