I need advice if anyone will read :(

One of my friends have been kind of depressed and kind of suicidal. She claims that when shes in school she fakes being happy because when she doesn't have a smile on her face all her friends keep asking her why she's in a mood. I'm not sure what i should do should I intervine or should I just leave it alone, you see I haven't known her as long as most of her friends but we have alot in common and the stuff we have in common her other friends do not (These things are like listening to heavy metal and watching anime) and she keeps these things a secret from her friends. I'm not sure weather she has told her other friends about her fake happiness or weather it's just me and my other friends she has told. You see my life isn't exsactly a bed of roses either i won't go into detail but it's been realy hard over the past few weeks for me and my family, I'm not sure weather i'm just emotionaly stronger than her but dealing with the issues i go through day to day with my family is quite simular to her troubles in a way so I can understand what it's like for her. -_-'' Any way I'm not sure weather it's my place to talk to her about these things or weather i should say that I'll accept her no matter what shes like or weather she should just continue to be happy around me as well, I mean surely she can't be faking all the time. Right? Please I don't know what to do D'X