Hi, Welcome to JustAnswer. I am a licensed veterinarian and I'm here to help you. I certainly know how we worry about our little pets. Starting antibiotics yesterday usually would not make much difference by today in her symptoms, but the fact that she is eating well indicates that she is basically doing quite well and is not in an emergency situation.
Tomorrow, if she isn't breathing more quietly or if she discontinues eating and drinking well, then I would certainly have her rechecked. Hope this is helpful for you, but please let me know if you have further questions or concerns.