We see many different definitions of love in Walk Two Moons. There's Sal's love for her mother (which is mixed with anger, too). There's the love between Sal's parents. There's Sal and Ben's new love for each other. And there's Gram and Gramps Hiddle's tried and true love for each other and for their son and granddaughter.
All these different types of love can get a little complicated, and Sal learns quickly that love doesn't always work out the way she thinks it will. It doesn't always move in straight lines. Most importantly, Sal learns that she can't take love for granted.
By learning not to be scared of things around her and things she cannot explain, Sal learns to love.
It is because Sal's mother loves her so much that she has to leave her.