Hon svarade nyligen den här frågan på Twitter :
Snape died for Harry out of love for Lily. Harry paid him tribute in forgiveness and gratitude.
There's a whole essay in why Harry gave his son Snape's name, but the decision goes to the heart of who Harry was, post-war.
Snape is all grey. You can't make him a saint: he was vindictive & bullying. You can't make him a devil: he died to save the wizarding world.
In honouring Snape, Harry hoped in his heart that he too would be forgiven. The deaths at the Battle of Hogwarts would haunt Harry forever.
Snape didn't die for 'ideals'. He died in an attempt to expiate his own guilt. He could have broken cover at any time to save himself
but he chose not to tell Voldemort that the latter was making a fatal error in targeting Harry. Snape's silence ensured Harry's victory.
(Ovanstående är texten till 6 tweets från J.K. Rowling.)