I think you're taking Gus' claim to lack agency too seriously. She seems to me to be using as a self-defeating shield, claiming to herself that things couldn't have gone any differently, that it isn't her fault her life is fucked up, that she was the 'wrong person' to gain immortality.
The key, to me, was the fight with the two jerks at the bar. She prefaces it by saying that it wasn't her fault, but theirs for offering violence. Then we see the scene... and it was totally her fault. She could have avoided it. She had enough self-control to set the keg down; that's enough self-control to walk out of the immediate area, too. She didn't. She chose to stay until a fight started and her berserk kicked in. Sure, she's got a bit of the werewolf curse thing going, but if you're a werewolf and you purposely stay out late during the full moon, well...
That's why I loved this one. Gus is so screwed up that she doesn't realize, fully, what she's done to herself, what she's doing to herself. She might never figure it out; she still thinks it was that place that was special, unique, magical, as shown by her unwillingness to go back and risk it failing her idealizations. She could have that again, but she won't let herself do it. That makes it really poignant for me.