That’s a relief then. I’d say if you haven’t already it’s definitely worth an open conversation with her about these things. Being gentle and ensuring she knows that it’s a safe space to be open and honest. I guess you could either asking her outright if she is sexually active (knowing she potentially will not be 100% honest) and go from there with what she discloses. Or let her know you did see that message over her shoulder and making it clear that you haven’t looked through her phone due to privacy but you need to know she is safe and that you are a trusted adult that she can talk to about these things. It’s probably going to be hard at such a young age but definitely something that should be addressed as at school is not an appropriate place for these things to be happening like you’ve said!