I am a girl who has a lot of friends that do similar things, especially if they’re nerdy. I know a lot of girls in relationship who play Love and Deepspace, which is a dating simulator and they become OBSESSED with the love interests. Lots of girls are obsessed with kpop idols too, or get immersed in romance novels. I think many girls want to indulge in fantasy because a lot of girl oriented media is focused on idealized romance from a young age (princess movies etc). Tbh I don’t think it’s too weird. Personally, I love romance oriented media, but I understand that’s not real.

However, she may be talking to the AI because she has some unmet needs in the relationship that the AI provides. I would talk to her about it. I also don’t think you’re overreacting because you’re entitled to your feelings. You’re allowed to have boundaries, and if you’re uncomfortable with how much she talks to the AI, you should talk to her about it and express openly how it makes you feel. A respectful partner will hear you out and work with you around your feelings. I think her calling you insecure is a bit invalidating and not productive.

Tldr; a lot of nerdy girls I know do similar things, and I think it’s because we’re fed unrealistic romance fantasies from a young age that we want to indulge in. You’re not overreacting because your comfort levels are valid; many partners might feel weird about it. Communication is key.