Should have focused more on Rosie
To me this movie had a lot of potential, but fell seriously flat in trying to portray a developing relationship between Jacob and Marlena. I'm not sure if it's the fault of the actors, the script or both, but it just didn't register for me, at least not enough for me to care about whether or not they ended up together. I'm guessing that this came across more effectively in the book, where we probably got more of Jacob's thought process and reactions. Here, it just seems to bring the entire movie to a slow crawl.
What did register is the potential for a more interesting story had Rosie been a catalyst for Jacob's growth. In other words, by getting Rosie to open up to him through communication and training (instead of sheer brutality as expressed by Marlena's husband), Jacob would understand more about getting Marlena to show her vulnerability to him. Marlena, in turn, might also respond to seeing Jacob get closer to Rosie. I think it fits, given that Jacob had completed his academic training and had experience on a farm, but obviously never with an elephant, especially one that had been abused (like Marlena, given her references to her past as well as her current situation). They kind of hinted at this type of attraction with Jacob understanding more about Marlena's horse than anyone else.
My guess is that the people behind this film focused on the relationship primarily because it's a major selling point, given Reese's stature as an actress and Pattinson's growing popularity. Too bad.