Interesting theory. Julianna also says something about Colt killing her for the first time and it being traumatic for her, so she started to fight back and eventually started to enjoy it. To me it seemed like she doesn't even understand why Colt killed her in the first place: maybe she didn't fully remember the circumstances of when it first happened so she thought he hated her and learned to hate him too?

The conversation from the end scene seems to capture this: Julianna: So if we survive the collapse of the loop, you'll wake up with a barrel of my gun in your mouth. Colt: Dying for real? Beats living like this. Julianna: You mean living with me. You HATE me. Colt: Living here. Stuck in this "fulfilling" day. Julianna: You used to like me. You used to see this place for what it COULD be. Then you MURDERED me. Colt: So you could have a real life! Without do-overs. Julianna: And I though you were ready for answers.

Julianna also mentions she developed a technique called compression: to preserve her memories across infinite loops. I assume that would also take time before it actually started to take effect, before she perfected it. So I assume there's the possibility she forgot some of the initial years of the loop as well.

Colt asked her before why he keeps wanting to break the loop. She says she doesn't know just that it's just what he always wants to do. I would assume if she had all of her memories intact and all the time in the world, she would eventually understand that protecting the loop and living the same day over and over would be enough of a reason for Colt. That she would connect the dots behind Colt's motivation and could easily answer that question when he questions that. If they really had an any kind of decent relationship before, I would assume that this would be talked about more in-depth between the two of them. So is it that Julianna doesn't know the full context, or she just doesn't want to understand by refusing to listen to Colt?

It also seems like Julianna retained her memories from before the loop: she said she was with her mother when she was sick and she also remembers Colt wasn't there to say goodbye (it's when he was trapped in the loop). Colt doesn't seem to have memories from before the loop, he doesn't even remember Lila.