My 15 year old daughter got bit by a spider. her doctor put her on antibiotics but it doesn't look any better. it's been two days since her visit.

Give it 2 more days: It should not look worse after 2 days of antibiotics. It will likely be more like 5 days to be noticeably better, after you started the antibiotics.

Spider Bites: In cases of spider bites that don't heal in a predictable manner, MRSA is often suspected and should be considered as a possible pathogen. You may want to consider obtaining an opinion from an infectious disease specialist if the bite is not improving.