She eventually comes to learn that Frank is not her real father, but this is years and years after her actual birth.
When last we left off with Claire and Frank, things weren’t super easy between the two of them.
The time-hopping narrative of Outlander has already shown us an adult version of Brianna, who saw that strain between her parents growing up.
While Claire had left her time travel narrative, well, in the past and decided to try and give her life with Frank another go, clearly things are still strained between the couple.