Does the school not have any counseling department? You should alert them about it.
That is very disconcerting as a parent. I have kids that both the high school one was at and the middle school the other was at had suicides last year. Painful and scary. It's difficult because we want a safe place for our kids to vent and tell us how they feel. I'd be concerned that this is your daughter's peer group just because some of that is kind of infectious. Not true depression but the attitude of negativity. But you want your daughter to feel like she can talk to you. At 13 especially, it is great that she still is. One thing I'd do is worry about your child first. Offer a therapist for her. I have one child who started therapy this year. He's highly anxious and I just felt it was time to work with someone who may have ideas for coping skills that I am not aware of. We go ahead and pay for this out of pocket because we had some insurance glitches finding the therapist we felt was best but if you have insurance and a way to get therapy for your daughter, talk to her about doing it! It can not hurt. I also think positive things in her life are essential too. What does she like to do? What kinds of activities can you encourage involvement in? Can she volunteer somewhere? Can she babysit and feel a sense of maturity and positivity from those types of activities? My theory in raising teens and tweens is to keep them involved. My sons do athletics but also clubs, etc. At 15, my oldest got his first job. I monitor social media. This doesn't mean I read all of their communication but I make sure they aren't involved in things that bring a vibe like a group texting situation that makes them feel bad.
If you fear anyone is going to harm themselves, I agree to reach out to the school. I have made a call before and did so making it very clear that I was protecting my son's privacy and they were to do so as well. They understand.
What about something where you get to know a parent or two of these other kids? Invite someone out to lunch or to get coffee? I text with some other moms and most are very open to hearing from another parent. If they are self harming, also, important to speak up. Does your daughter do that?