Chapter seven: Rainbow Dash.
Rainbow as a human was actually an athletic girl with retired athlete champions as a dad and a retired jet pilot as a mother. She loves the sports and at the start doesn't like books because her memories mostly are about sports and athletic activities.
In the human universe her clone loves sports and is seen as being quite good at them.
Rainbow's first race helped her mutation settle thus she created the sonic rainboom that became a so called 'old pony tale' when she performed it. She also had her mutation settle enough for her mutation to allow her to gain her cutie mark.
Her father had a pet tortoise and Rainbow with her love of speed began to feel creped out when Tank began trying to win her affections…. When in truth he was once her fathers pet sent by the scientist in hopes to make Rainbow remember her old life then in hopes she would return to her old life.
Yes Rainbow doesn't get remembered about her old life but she holds a strong affection for Tank more so than expected than from someone saving them because she allowed Tank back into her heart.
Rainbow may actually be one of the last ones to truly remember her old life out of the main six.