looking for advice on a dark family issue

About two weeks ago, a cop came to the door looking for my sister. She's 14, soon to be 15, and I guess she said to a friend via fb messenger that she's inclined to self harm or possibly worse. :,( the whole thing is really heartbreaking.... But I'm worried my parents aren't taking it seriously. Any time the subject comes up my mom expresses anger at the fact my sisters "needy" friend "turned her in", basically calling him a drama queen. It's very possible that I don't have all the right information because Mom is an incredibly compassionate person, so I'm surprised she would react this way. I've heard nothing from my dad. How do I navigate this without causing unnecessary tension? I want to keep a cool head and an open mind in order to love and support my sister but I'm starting to unravel a bit and I feel like I might snap at the next asshat who crosses my path 😂