I understand, dash. I spent years trying to understand "why" Oldest would tell such outrageous lies (your stories strike a chord... Oldest once called in sick to work telling them her sister had been hit by a car.. not true). I finally had to accept that there was no "why." None that I could understand, anyway, let alone change or reason with. If you've not dealt with this type of lying, it's very difficult to relate to it. I've had well-intentioned friends offer to "talk to" Oldest, thinking they could "get through to her." It just doesn't work that way when you're dealing with a personality disorder, unfortunately.
You're right, this is her issue, not yours. Hugs.
You're right, this is her issue, not yours. Hugs.