As for the strategy, while Tron finished her off with his Number card, I still think that she made it extremely easy for him to do it. I also still doubt that it was a well thought out plan because, despite all of her efforts to boost up her life points and being fully aware of how dangerous Tron was, the strategy she made was pretty risky and she didn't have much of a backup plan in case her strategy fell apart. Maybe she was so sure of her strategy or thought that she would strike too quick for Tron to do anything about it, but in either cases, it would be a significant hole in her logic due to Tron being so dangerous.
EDIT: Regarding the love interest issue, I just want to make clear that I'm not against the idea of female characters developing romantic feelings for a main character. There are anime pairings that I like and JackxCarly from 5D's is one of my personal favorites. The problems I have with the love interests in Zexal is that they aren't shown as anything more than love interests and that their relationships with the main characters have not lead to significant character growth for either one of them. One reason I like JackxCarly so much is because they both received a lot of development through their relationship and growing romantic feelings for each other, especially Jack. Although, Carly did become not much more than a Jack fangirl post Dark Sigenr arc, which I didn't like either, but there is more depth to their relationship than what little one could argue there is with Droite's relationship with Kaito. If they had more meaningful interactions with each other that led to development for the both of them, then maybe I wouldn't have as much of a problem with it. As it is, the relationship feels poorly handled and I don't see any reason to feel invested in it.