Wait a second... You play the flute? That's cool.
I play the trumpet, trombone, euphonium, tuba, saxophone, oboe, clarinet, piano, and percussion. Just about every wind instrument (Plus a few extra...) except for the flute.
There is such a thing as a double flat, it looks like
Personally, I've never seen one in a piece of sheet music, but the next song I write will implement a few...