Originally Posted by v2micca
Why did Arya not use one of her three deaths on Tywin, and why was Tywin simply sitting around at Harrenhaal while Rob was raiding his lands?
For the same reason she didn't in the books. She's a young girl who is attacking people being mean to her, not being militarily strategic. It's a huge part of her character through the whole book. She does things without thinking through her actions and their consequences.