There was an article on the Crimson about a girl who got in after being homeless for a big part of her high school years I think. I’ll look for it.
Edit: Not the story I was thinking of but here’s another http://www.jeannineamber.com/uploads/cgblog/id22/homeless_to_harvard.pdf
Here’s the story I was thinking of http://www.businessinsider.com/most-impressive-harvard-students-2012-11#dawn-loggins-overcame-abandonment-and-homelessness-and-still-made-straight-as-10