Headcanon :)
Hermione was homeless from the end of the Goblet of Fire. She obliviated her parents after Voldemort returned so they would be safe. Now I know you're going to say 'but we see her obliviate them in the Deathly Hallows', but this could be footage from at the end of the Goblet of Fire.
After all, from the Order of the Pheonix onwards, she spends all her time at Grimmauld Place, the Burrow or Hogwarts. And when she wasn't at any of those places, I would like to think she was working as a waitress in the Leaky Cauldron in exchange for a place to sleep. So not really homeless, but basically homeless.
And I think this played a part in her decision to go with Harry and Ron. Sure, it was mainly because she wanted to defeat Voldemort and the boys would have died without her, but otherwise she would have to choose between torture at Hogwarts or living on the streets in the Muggle world (seeing as there were Death Eaters all through Diagon Alley).
I know this was really sad, and I'm sorry.
