OK, thanks for the extra information.
We actually do use erythromycin in dogs. The normal dose is up to 20 mg /kg which in your dog would be 227mg. So, if I was dosing your dog with erythromycin I would actually be prescribing 250mg twice daily. Therefore, a single dose will not cause any problems. There is the odd animal that can get some stomach upset from erythromycin, but a single dose is unlikely to cause concern.
That being said, the erythromycin will do nothing for a red eye. If the eye itself is red and swollen your dog may have glaucoma which is a serious problem and she should see a vet soon, even tonight if possible. If the area around the eye is swollen this could be due to a bruise or infection and if it is not improving within 24-48 hours she should be seen. If the white of the eye is very red and the dog is squinting this could be an abrasion on her cornea and that requires emergency care as well.
I hope she does ok!
I hope this information helps! If you have more questions regarding this problem, just hit reply. If I am online I will respond right away. Otherwise I will respond as soon as I come online again. Or, if my answer is sufficient, then please hit accept. Thanks!
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would highly advise contacting your regular veterinarian.