[Of course Jack shouldn't be the one she's kissing, but what can she do about that with the bots around? It isn't worth getting crushed over and as much as she does hope things are heading back to a romantic place with Reid, she trying not to assume it can. Reid has been through a lot—they both have—and just because it's something she wants doesn't mean it's something he's ready for...or wants. So, for right now she's still single. She's just not actually looking to mingle because there's hope and she doesn't want to throw away her shot.
Jack isn't the first and won't be the last of her non-Reid kisses today. He may not even be the most emotionally confusing one, but he definitely ranks. He always does because there's always that something about him. The future pheromones. The swagger. The heart. The partnership in the Force. The years of experience just making him really good at this. And, of course, those false memories of a day spent completely in love with him with the promise of a figure together etched out before them.
It makes it hard not to respond to this. Kissing him is familiar and exciting which is an intoxicating combination. And while the mind, heart, and body work well as a team they can also have their on individual selfish needs and this sort of event certainly brings out the ones her body wants. So maybe she can be forgiven if she parts her lips to deepen the kiss or presses in nearer to him.]