Strange Confession

So I am a boy at the age of 17 and she is 7 years older than me.
I was almost a random person to her. I've tried to chat with her
but things werent going well so i decided to confess to her. She rejected me but said we can
be friends which i gladly accepted. But i dont think she really likes me(even as a friend).
She never texts me first and when i text her the conversation isnt going smoothly(she is
just repeating the same questions i ask and isnt very talkative to me) so one can assert
that i am even disturbing her. So i want to make one last try. I want to go out with her
(which i have tried to persuade her before but didnt succeed) and confess her something.
This something is really strange. So basically i know things about her (bad things about
her mentality that an outsider shouldnt really know) that she thinks only her parents and brother know.
Her cousin told me that information and i really dont want to put him in any danger of
deteriorating relationship with her family.
So i want to confess her that i know of her life and these shameful secrets of her BUT even
though i know them i dont want to leave her alone and i want to be her moral support. And
even thats even more reasons to want to get closer to her. And i just want to be friends at
first, will see later.
How do you think she will react at this bold and shameful statement?
What to do to maximise the chance to accept me?
What should my friend/her cousin do if things dont go well?

Thanks in advance!