Are you kidding me??? How stupid and selfish can a person be??? Even animals get treated better then this!! Why should it remain a secret??? So she doesn’t no where her DNA comes from??? SO when she grows up and is trying to have kids, she is giving the wrong famillyy history??? This mentality is disgusting.
And I don’t even know on how many levels, but this has to be soo wrong in Islam!!
Of course she was gonna find out one day, 
. I’m sure they did this to “keep her safe,” well what a great job!!!
But now my question is why are they STILL being soo stupid and selfishh? They need to tell her the truth straightforward,instead of coming up with a game plan. And apologize for the past, and then give her, her space! It might take her 1 month or 2 years, but she is gonna have to deal with this mistake of her parents own her own! But the good thing is that since I’m sure they were good parents overall, she will come back to them one day emotionally. It would have been much better if she was told gradually. But for right now her entire world is going to be upside down, and there will be nothing that anyone can do, this is her fight!
And this is so sad!!!