Are people naturally smart or do they try harder?

It's summer and I'm in university calculus 3 right now and there's this really smart high school sophomore next to me who I've become friends. This girl doesn't seem to take the class too seriously and always seems to be happy. She's easily acing the class while I'm just struggling to pass--even if it's a subject I enjoy. Also, she works amazingly fast through hw problems just recently assigned while the professor is lecturing and always seems to correct his errors. When I do my hw, I get stuck often and have to take time to think over my mistakes, but she breezed through each problem during class.... When I study with her and her friends they never seem focused, but always chat and get off task. If I ask her a question, she seems to know the answer every time. And although she claims to not be sure, it is always correct when I look it up later. I'm really jealous of her aptitude right now... especially since I'm studying so much yet always score lower than her every time. It gets me wondering if people are just born smart.