She'd try it. Keller took the seat next to her, and it was definitely simpler to read him - read someone she knew - and try to play that to her advantage.
Annie simply knew how to count cards - didn't work so well in poker, but it was tailor made for blackjack. She did her best to try to make her luck seem natural - occasionally hitting when she knew she would bust - and after a while, noticed that when Keller moved his hand a certain way before motioning for a card, he would invariably bust. If he was doing it on purpose, he was smarter than he let on, and if he was doing it unintentionally, it was just as handy. Not like she wouldn't use a decent part of her winnings for something he'd enjoy, not just her.