how to help someone whit depression?

Alexis
Earlier this school year my cousin told me that she might have depression (told by a school counselor) but she hasn't been clinically depressed. She also said that she tried to cut herself once. No one in the family believes her because she lies about everything. And when she told us she said it like she was reading from a grocery list. And the school counselor never contacted her parents. So with this there was no real reason to believe her. But today she told her brother that she wanted to kill herself. So now I think that she was being serious. My cousin has a really outgoing personality and by the way she acts she doesn't seem depressed. But if she really is I want to know how I can help her.