It depends on what she had. You could ask to talk to her doctor about it.
Yes, I think you should ask the doctor. I feel like they are good to go if they have just something treated with antibiotic---- two days into it. But if it is secondary to a virus, then longer is better. Preschools usually say that they want kids to be done with their antibiotics but that is not realistic for 'real' school (kindergarten on). good luck