I think that photo shows a bit of JonBenet's personality, or her desire to perform, or something that she expressed by, as BR terms it, "flaunting it." Was she performing for the camera? Seeking her mother's (and maybe her father's) approval? Or just expressing her own personality and joyful nature? We could have known by now, if she had lived. She might have gone on to become a Miss America, or maybe she'd have ditched all of that and just lived a normal life, going to college, having a career, getting married and having her own children.
It is my feeling & belief that BR probably resented his sister from the start, that she was an easy child to love, whereas he had his quirks and challenges. It wasn't the bike, if she got one and he didn't, but more of who she was, that he resented. That to me, was the motivation for the act(s) that he inflicted on her, and the fact that he had no remorse afterward.