Rose had noticed that there were no mirrors on the TARDIS, besides the one that hung in her bathroom.
At first, when she hardly knew the man that had whisked her away, she thought nothing of it.
As they spent time together, she slowly realized that it wasn't a coincidence.
They said that mirrors were the windows into one's soul.
His soul was too broken for him to look at without seeing the hate and so he avoided the sight. He could not bear to love – to know - a soul so tattered.
And so she loved it for him.