Backstory: It is unknown when Lizzie was created, but she was sometime created by Robotnik in a lab, where she was tested on since she was a hybrid, part cat part human. As a result, Lizzie has intense PTSD and no longer likes science. Thankfully, when Robotnik first discovered Sonic, Lizzie decided that it would be the perfect time to escape, and thankfully she did. But she wasn't found by the Wachowski family until after the events of Sonic movie 2.
Other: Lizzie has a habit of calling people "Ma'am" or "Sir", including other kids too. It may take her a while for her to get rid of the habit. She also has a permanent limp, making her slower than others. But she can still run and walk just fine.