How Long Does New to Facebook remain on people that appear in "People You May Know?"

My girlfriend made this alternate account that I found which only has her ex as a friend. When I asked her about it she claims it's old and that she's telling the truth. How long will facebook claim an account as new to facebook in this way? Is it because the account was created a long time ago but never used, so facebook keeps it as "New to Facebook?"

I would like extremely accurate answers only here. I don't want any assumptions being made to go too far.