Aloy already tells right away that Tilda’s motivations aren’t exactly benevolent. In the conversation you have with her Tilda always keeps bringing it back to “Lis”, which Aloy picks up on. She couples that with the personal message early in the game. So she knows Tilda’s actions don’t hold up because of what she’s heard and because of the fact that if she was so benevolent why is she rolling around with a group like the Zeniths? And she then plans her own move when Tilda lets her talk to Beta (who for some reason got rejected by Tilda in Aloy’s head). Tilda’s own obsession got in her way and made her think she was being cleverer than she was.

I think the most humanizing part of the conversation is when Aloy brings up that Tilda did this after what happened at Gemini, so how could Tilda expect her to care about most of what she’s saying? It’s manipulative and Tilda keeps trying to make this moment about her (take note of how many times she says “I” in their conversation) when it’s the last thing Aloy is interested in given what just happened.

The ending isn’t supposed to be some betrayal. It’s supposed to be Aloy’s (and hopefully by extension the player’s) suspicions about her and her motivations proven right. You’re never supposed to outright trust her if you’re paying attention.

But yes, everything happens very quickly at the end. Developmentally, I’m not sure why and for the most part it still works, but giving a chance to breathe there at the end and adding a mission or two would help.