Her friends all know she's different. They hide the truth as well as she does. She's always come across as normal. Someone who fit in, got along with everyone, and was just all in all, a good person.
The act she puts on, is so good, that you can't tell it's even there unless she tells you. Or better yet, shows you. The facade is so believable, so real, that only those who know her best know what her reality's like.
She won't let herself cry. Crying means giving into weakness, which isn't a trait she'll allow herself to exhibit. She wants to be fearless. She doesn't want it to be possible to impermeate her tough exterior that she hides behind, using it as a shell.
She's not fearless though. She's afraid to let anyone in. She's afraid she might not be able to let go. She's afraid of people knowing her too well. She's even more afraid, because she knows all this has already happened.
Her friends know her secret. She didn't intend on that happening, but regardless, it did. They know that the truth could destroy her. They know that the truth does destroy her. But they'll never tell. Nobody can know, because nobody would understand. They don't even understand themselves.
The only real trait about her, the only thing that isn't fake, is the deception she hides behind.