Thanks for sharing that, I'm sure it's not exactly a pleasant exchange at all, leave alone that it's your own sister.
Something caught my attention, and as I have mentioned before, reasoning with them about facts and teaching may bear little productivity. However, I do notice in her conversation that she ties up her believes with your father. Seems like he's not alive. To me it looks like she's been more loyal to your father's legacy than to the WT teachings.
Maybe if you address what she's implying about what she feels instead of what she says about the WT teachings may take you in a different direction.
Either way, as frustrating as it may look, it's also possible that this exchange may stick and may become relevant for her in the future. You just don't know.