Yes, talk to her, and ask her if she would like to talk to someone, like a therapist. Explain that it can be so cathartic for her to be able to talk to someone who doesn't have a direct interest in her life, to get unbiased opinions and advice.
Maybe she will open up to you about how she feels, or maybe she will tell you she WOULD like to talk to a therapist. Best of luck...def stay on top of it, keep an eye on her!
Definitely look further into it, ask her how she's feeling, if she feels depressed, etc. How old is she?
Should I do anything about this? Bring her to therapist or psychiatrist?
She is ADHD, if that would have any effect.