I have read all 7 books and seen movies too. One thing in mind that i want to ask all of you,
If you read all books carefully you will find in all books house elf's and Hermoine are linked with each other.
Even Hermoine expresses her emotions towards house elf oftenly.
Also in Book 7 when Ron cares for house elf to give them a chance to escape, she kisses him.
She has started SPEW.
In movie 3 prof Trelawney says she has a heart of old house made.
OK, now in book 6 in story Hepzibah,
While Riddle was visiting her on behalf of Mr. Burke, she imprudently showed him Hufflepuff's cup and Slytherin's locket. Two days later, she was found dead; poison was found mixed with her cocoa. Riddle was never suspected; Hepzibah's house-elf, Hokey, confessed to the crime.
so i am thinking that house elf Hokey takes rebirth in form of Hermoine Granger and helps harry to destroy Lord Voldemort.
May be J K Rowling will talk about this in encyclopedia.