Sarada's sun MS represents the balance of yin and yang energy. The sun is a yang symbol symbolic of physical energy which she displayed plenty of during her fight with the Shins. As an Uchiha she inherits yin energy from the sage of six paths. This is speaks volumes because the major theme of the series has been the battle between yin and yang, Ashura vs Indra, Madara vs Hashirama, Naruto vs Sasuke. This leads me to believe that Sarada represents a new dawn for the Uchiha. Her father Sasuke was meant to be the atonement for the curse. Having to bear the hatred within himself before purging it during his battle against Naruto. But through his offspring the destiny of the Uchiha will be fulfilled. On her road to Hokage she will be the light in a history of darkness for her clan. Hence the sun MS. It was Hagoromo blessing Ashura with the six paths chakra and appointing him as successor that began the cycle of hatred. Now that the cycle is broken the destiny of the Uchiha is to be fulfilled through her as the one who would not fall into darkness but ascended into new heights while shouldering the legacy of her clan.