Those teen years can be so difficult, on so many fronts. You’re exactly right that she’s exploring, and I’d imagine that for her, the religious element is the tiniest part of the equation. The bafflement of first dates and kisses, trying to navigate jealousy and what’s “cool” or not. Hanging out in big groups or being alone with a crush for the first time. It’s pretty confusing.
I’d strive to make Judaism the safe space. The thing she can come back to with a broken heart or complicated friendship. An oasis. Because even when kids seem to be pushing away, they also appreciate comfort, the familiar. Even if they don’t tell us.
I definitely wouldn’t be critical of this guy, but is it possible for you to give her some discreet Jewish experiences beyond school? Family camps, youth groups, or Shabbatons? Social events like that might be a good way for you to continue her Jewish education without seeming to compete with her new life in school. I know that when I was a kid, camp was such an important relief from the social/peer issues at school. It was like summer was a blank slate, and I could try on new selves. I often came back to school with a brand new “style” that I’d adjusted to over the summer.
Also, if this guy sticks around, I’d encourage her to include him in your family religious life. Be as welcoming as you can. You don’t want to set this up as a competition, and if he’s uncomfortable with your rituals, your daughter will see that, and think it over. This guy isn’t going to be around for very long, I’m guessing, but this moment is formative. How your daughter chooses to define her own Judaism—as integrated with her secular life—may ripple into adulthood. Above all, I’d try to keep it positive.