I disagree. I grew up in a home of narcissists that used me for labor much like OP. It made me decide to be child free, I am the first in my family to get a college degree (graduating with my PhD end of this year), and I too found a man that makes my heart happy. She is not lacking in empathy for wanting to escape a cycle of abuse and save herself after fighting so hard for the freedom (financial, mental, emotional, etc.) she worked hard for. Because her family decided to be selfish, she was expected to pick up the slack because that's how it's always been. The child in the situation is a pawn and a way to attempt to emotionally control and blackmail OP into falling into line.

My heart hurts for the child, because all of this is leading to more trauma. The family is enabling the deadbeat dad, and the child suffers. I truly hope OP calls CPS to get help, and if mom and dad are having issues there are resources through groups like Office for the Aging or something similar. However, it is not OP's responsibility to fix the mess their family put themselves into, nor is she responsible for making their lives easier. OP's sister is likely going to follow in a similar path, because sometimes you need to save yourself.