In Lyddie by Katherine Paterson, why does Lyddie feel envious in Chapter 18, and what does she do with that feeling?

At the start of Chapter 18, Charlie has come to visit Lyddie.  He tells Lyddie that he has a very good life living with the Phinneys.  He gets to go to school and live in a house with a mother and father of sorts.  He gets to be "normal," and he seems quite happy.  Additionally, the Phinneys would like to take Rachel on as their daughter, too.  The entire situation makes Lyddie feel jealous, because she has been working her fingers to the bone to try and scrape up enough money to keep the farm and pay off all of the family debt.  She's envious because she feels that she is doing all of the work and Charlie is the one getting the good life.  

Lyddie doesn't do anything with those feelings, though.  She quietly swallows her thoughts and allows Rachel to be taken back to the country with Charlie.  The feelings of jealously do not last long, but they are replaced with all around depression.  At the beginning of Chapter 19, the reader sees Lyddie struggling to find a purpose for herself at all.  

My heart is heavy, she thought. It’s not just a saying. It is what is— heavy, a great stone lodged in my breast, pressing down my whole being. How can I even stand straight and look out upon the world? I am doubled over into myself and, for all the weight, find only emptiness.