An antibiotic for THRUSH and for a virus? Antibiotics don't work for either illness. Sorry for saying so, but this doctor has a lot to learn. Antibiotics cause the friendly bacteria to DIE which causes yeast, which is what causes thrush! Time for a new doctor.
There are probiotics (good bacteria) that you can buy for children in liquid form and have them drink. Another thing - cut out ALL sugar and white flour products. These will make it much worse. You can also read the book "The Yeast Connection" to find out more about it.
Make sure your daughter is staying away from food allergens - which can be a source of digestive problems which cause yeast (which causes thrush). When I eat wheat or dairy, for example, I don't know what happens, but I end up with major yeast problems. Yeast can show itself in vaginal yeast infections, thrush, itching all over, and even cause flu-like symptoms! Then I have to take major probiotics.
Make sure she doesn't drink milk with hormones in it and stop the antibiotics. You didn't mention if you are still breast feeding or not. You can take probiotics (friendly bacteria) with high potency and pass that to your baby as well.
The food companies LIE when they say that the antibiotics in meat and dairy don't affect children. AND they lie about genetically foods not affecting children. They have actually fudged their "scientific" findings to make the bad data go away. The less we feed these things to our children, the better. Now, unfortunately, they are using GMO beets to make sugar. So it's hard to say what caused your daughter's thrush. Maybe her sugar consumption went way up. Also, MDs generally only have about 5 hours of nutritional instruction in their education.
After making sure she doesn't have food allergies and probiotics have cleared up the thrush, if I were you, I would buy a lot more organic produce.