[X] Charm. Look, you are a loner by nature. The company of others has never really appealed. This Human might be intriguing, but if you're going to consider striking up a friendship, they're going to have to find a way to convince you they'll be sufficiently fun to spend time around.
Okay, so, let's particularly look at this. All three of the options are not just a case of what Trixie is looking for, but also how she feels about humans more generally in this moment.
Intentions is the option that leads to the most paranoia, the most fear of them, the instinctive wariness that means she's looking for a reason to mistrust her. I don't want that. I think there's a risk of her getting too one note, especially when interacting with a human who doesn't have any Pokeballs (and given she's using an old, pre-owned one, she's not well off).
Determinations, by contrast, is the passive-aggressive option. It's not just that she's looking for determination; it's that she's pushing the human hard to keep them at arm's distance, because she's an arrogant little thing who expects them to fail her challenges.
Charm is the most attractive to me option at the moment. It says that Trixie is looking for reasons to hang out with this weird human who treats her like Ash does, who is interested in her and talks to her like she's a person. She's willing to contemplate this because she's been disarmed, yes, but she's also curious (especially after finding out more things about the world and all the nice things that can be obtained from PokeMarts) to interact more with a human who can't catch her.
After all, Trixie's just been deprived of her main hobby (tormening trainers in Viridian Forest) and therefore will want a new way to entertain herself.
(also, her little sister is adorable, and Trixie is clearly educating her to be an adrenaline junkie menace too)