8: Malon uses singing as a coping mechanism. In the child timeline, she sings at night at a Castle Town Market. She’s alone, and a child. She’s scared, so she sings. In the adult timeline, prior to Ingo’s defeat in rescuing Epona, she only sang at night I’m the corral. She doesn’t want Ingo to know she’s singing.
Once you save Epona, she sings all the time. It’s no longer really a coping thing, instead, it’s a symbol of freedom and hope. At least that’s how I view it.