So I went away for a few days and had my grandma take care of Lily for me and now that I am back Lily is so angry. She actually bit me when i got home to greet her. Almost 90 % of the time I try to go in her cage she will flap her wings and crouch a little and then hold her wings in the air.

I know this has to be agression haha - but will she forgive me? Before I left she was happy and loving as could be and now she's furious and biting.

What exactly does this wing flapping mean?
Also, how can i tell a happy purr vs an angry purr?

That is exactly what Kiwi did years ago.......Just wait a few days and she will be back to her old self. She is just paying you back for leaving her.....

An angry purr is a chattering growl...Like Sandi said, give her a day or two and just keep loving on her, she'll be back to her normal self soon.