Jealousy

In the book, Stranger With My Face by Lois Duncan twins Laurie and Lia were separated when Laurie was adopted.  While Laurie ended up with a loving family in a big house, Lia's childhood was tough and she ended up in a mental institution.  When Lia visits Laurie through astral projection, she tries to take over Laurie's body and life, harming many in the process.  This makes me think that that the author is really trying to portray the dangers of jealousy.

I think this because of what Lia did to try and lead Laurie's life.  For example, she was willing to let Laurie die off in order to have her life.  When Laurie's boyfriend started to notice that she was acting differently, Lia tried to use Laurie's body to lure him to a dock so she could drown him.  Overall, Lia was so jealous of Laurie's easy life that she was going to hurt others deeply to get that life instead of changing herself to be a better person and making her own life better.  This also makes me wonder about why some people are blessed with an easier life than others.  Why are some born rich and others born into starvation for example?  Is it fate?  Or can our actions really change our entire lives?  Maybe if Lia had chosen a less cruel path, she wouldn't end up as she does in the end. (I don't want to give away spoilers.)   Or maybe, she was destined to that end.