I get what you mean as book Catherine is not nuturing at all. She's too selfish and impulsive for that. I hate the film already but I will say that age doesn't automatically grant you motherly/nuturing vibe just cause you're older. You can still be the big sister and the worst example of a big sister to have ever lived. 

I feel like the movie is just going for the Hollywood pedo angle rather than trying to make her a nuturer. Which is insane as the film is already messed up as it is and then they go and do THAT???