Dolores recognized Caleb’s ability to make non-monstrous decisions when he was the one soldier in his unit who spoke up against raping all the female Hosts that were “saved” in the training exercises.
Westworld dropped the reveal that the ever-mysterious Park 5 was actually used to run military training programs, which Caleb was part of.
Yes, Dolores was one of those Hosts, and that was one of the moments of beauty that she chose to hang onto, as opposed to all the ugliness.
For those wondering why Dolores picked Caleb as her Judas cow (a callback to one of Dolores’ scenes in the series premiere), it was because she’d actually crossed paths with him years earlier.