Ooh, well wouldn't that have lost the whole message of Mockingjay? Not to mention that it was the filmmakers fault, not the book's fault, that MJ1 wasn't as critically received as the first 2. They changed more than you'd think in the book, lol.
I believe that it was mentioned somewhere else in the boards, but Katniss wasn't all googoo eyed and cry baby over Peeta in the novel. She was reluctant because she blamed every live lost on her actions (District 12, D8, etc.) Peeta was just one of the main ones caught up in her mess. I guess the screenwriters just wanted to focus on the love triangle.
As for the action, she wasn't supposed to "shoot just one arrow the entire movie". She shot down hella planes and so did Gale. I honestly don't know why they narrowed it down to one dramatic shot, its not like they had a low budget. Plus that camera angle was awful. So many movie fans thinking that she was the one who blew up the hospital, lol.