I have two theories regarding Charlie.

Theory 1: Charlie's a nephilim. the personal reason is because she looks taller than her dad and nephilims have been described as being tall and strong. It's also worth noting that she is The offspring of Lucifer, a fallen angel and Lilith the first woman.

Theory 2: Roo is her true mother. a lot of people with theorize this and I am here to give my reasons. When in her demon mode, it's visibly different from Lucifer's as it appears more reddish pink like Roo's and her hair flares wildly like fire similar to Roo's. They also have the same nose and same body build. Plus the Creator herself said she couldn't answer a question regarding if Lilith and Lucifer were her true parents