OK, wow. Not sure I'm on the right case. Dad did know- Anna is… well, or I guess, she was an angel. Apparently without their grace, they're sort of like humans, and that's what happened to Anna. Now, all we know is she was an angel, somehow lost her grace, and has grown up thinking she's human.
Anna might kill me when she finds out she's an angel. I have no idea. I'm sure it wouldn't be a fun playdate. Bobby's on the Winchesters' side, so if I tell him what I know, he'll just tell them. I want to see what they figure out on their own. Besides, I don't know what happened to Anna's grace, so she's probably happier not knowing she's really an angel. She should just try to live a normal human life while she has the chance.
Bonus question: Alastair is after Anna. Do I want to know anything about him? Maybe, maybe not. Dad makes it sound like he's a real creep and also pretty dumb.
But, if I skip the case, Dean and Sam may not offer again, and I'll be letting Bobby down.