1) If Annette was the mole, why bother making it seem like she's investigating it? Wouldn't that tip her off? And why would Annette have said that she'd reveal the results on Monday? Annette was Jeff's most loyal worker, perhaps he genuinely thought she was the best person to investigate the leak since she was his first employee.
2) I agree that this is probably not why she was killed. I agree with the SD card theory, too. However, I'm not sure if Annette was the one who put the clock there and has the card. I had wondered if Darren put it there to spy on Annette because he had been hearing about her with other men. He got really hot under the collar at even the suggestion of her seeing anyone else.
3. That's an interesting idea about Jeff, but I don't see where anyone named Banks mentioned something about Jeff's car. All the interviews I see under "Crime Scene Canvasses" don't mention Jeff at all except for Gin Tessi. Although, you do have me thinking that all know about Jeff's timeline that afternoon is what he told us. I still think it looks a little too obvious, though. I will check the new information and ponder some more.