Poseidon's tears considerably strengthened Shen Shen's already powerful soul, it also cleansed her body of any impurities. The girl's Lvl or Realm remained non-existent but her foundation was solid and perfect so if she embarks in one of three orthodox strengthening routes, she'll power-up at an absurd speed. In fact, Zaarae said that by the time she reaches twenty and if she trains diligently, she'll become an Overgod or a Lv10,000 player.
Surprisingly and despite the Empress' objection, Shen Shen wanted to become a player as cultivation seemed too boring for her taste. She's the curious and adventurous type and killing mobs to become stronger is much more fun than cultivating in an empty cave for months or even years.
So, Zaarae ended up providing a personal system only meant for the little girl as, per her words, the universal system isn't that good and could possibly endanger her later on.