My sister just told me she had intercourse for the first time. What do I say?

Hello Reddit, I need some quick advice because my little sister just told me she had intercourse with her boyfriend of a year without a condom and I’m trying to figure out how to talk to her about how dumb that was. They’ve been dating for a year and have known each other for 3 but they are in their early teen years so I think it was risky of them to do that and I wanted to know what the best way to approach it is without her shutting me out. Any advice? I’m going to talk to her in an hour or so, so any advice helps please!