Dear Melinda:
You described an unjust situation at work: you and the co workers you mentioned are paid the same, yet your work load is double or so. The supervisor doesn’t perform her job (and is probably gets paid more than you). Unjust and unfair.
At the end of your post, you wrote that you read all those books and you: “can’t understand the purpose of this situation and what I need to do to get out of it. To what end? I know my life is happening for me not against me but seriously this is slowly killing me.” “To what end” is also the title of your thread.
My answer: there is no purpose to this situation and your life is not happening with your welfare in mind: there is no godly manager that created this particular injustice for you personally for your own good. Looking for that good is not congruent with reality, I believe.
Injustice is what happens in life, a whole lot, everywhere. Unfortunate but real. It happens because of ignorance, laziness, ill intent, aggressiveness, and so on.
You tried to solve this injustice by approaching the manager and you did well. Unfortunately, as you described, she is not very involved and is less than competent. What do you do next?
anita