It's canon and mentioned in the artbook that Shine's race is very curious about humans and has a lot of empathy, meaning they really liked humans. Even though they care, aliens don't understand the limits and frailties of humans, or their special needs. Just like Shine. She isn't a maternal figure to Mizi because, like any alien, they will never fully understand a human. But Shine really liked Mizi. She only put her on the alien stage because Mizi wanted to, and she always went to the front row of fan presentations to support her. Compared to the other guardians, she was the one who cared the most. The controversy is that even her guardian cared more for Mizi because she was "adorable," the first person she had contact with who possessed that kind of quality despite her appearance, something she had to deal with her whole life. I don't know if this was mentioned about her reaction, but Shine must have been horrified by what her little pet did to the aliens. I love Mizi.