This was not like anything I've yet to 'uncover'. Also, while you think you did not stop the car, clearly both of you and the car were stopped somewhere in time or space. Your description of the UFO having a reflective quality similar to the environment has been a theory proposed by researchers and non-researchers alike. That would enable the UFO to visually acquire the qualities of the surrounding environment. Also, your not discussing it with your sister or family is typical.
Many people are unable to explain years later why the subject was never discussed.
However, now that you are probing it, you may begin having flashback memories or even dreams at night of what really happened. Also, the balls of light are known to communicate with people. I do feel like something was definitely trying to communicate with me. I couldn't tell many about this, they'd think I was bonkers, but my parents understood. It struck me as odd, though, because my sister left around 1 p.m. in the afternoon.