In a Walk Two Moons why does Sal feel frightened at the Wisconsin dells?

Sal feels frightened at the Wisconsin DELLs because she sees the sight of Phoebe's mother kissing a man who is not Phoebe's father, and this unexpected revelation shakes her perception of family stability and truth. Additionally, the DELLs remind her of her own fragmented family and the uncertainty that lies ahead in her own life.