I’m really worried about my friend?

My best friend is having a really hard time lately. She’s in a lot of really hard classes, she’s been having family issues, etc. tonight, she went out with some friends. I had snap chatted her around 7 p.m., and she’s usually pretty good about responding, especially when she gets home around 9:00ish. She never opened my snapchats, so I assumed she was with her boyfriend. Around 11:30, her boyfriend called me asking me if I had heard from her because her dad had called him asking if he knew where she was. Again, she usually isn’t one to stay out late or not answer her phone. She got home from hanging out with her friends close to midnight, and I asked her where she had been. She got really mad because she thinks it’s ridiculous that she’s an adult and she thinks she should be able to stay out past the time she usually gets home without people worrying. I’m not worried about her doing anything she shouldn’t have been, but I am concerned. I told her we were all worried because this isn’t like her, and she said she was upset that we were more concerned about the where she was than the fact that she hasn’t been okay lately. I told her I felt like an awful friend and that I am sorry. I think she went to bed, but she hasn’t responded. What should I do?