With the fact Fey had carried a long-term affair with Bradford Meade, Amanda worried Bradford may be her biological father since it would mean she had committed incest by sleeping with Daniel, who would be her half-brother.
Amanda was worried that since Fey had an ongoing affair with Bradford Meade, Bradford could potentially be Amanda's biological father. This would mean Amanda slept with Daniel, making him her half-brother and suggesting she committed incest.