Alice was/is the host of Zero, they used to be friends as Alice would always get bullied, but when she got beaten one day she passed out and continued to pass out until Zero took hold and eventually gained control over Alice's body, making it her own. In the comic Alice isn't actually Alice as it's Jeremiah portraying what Zero lost, "she" (Alice) is portrayed as manipulative in the comic for the brief moments she's in the pages.

I imagine her voice to be slightly softer and sounding like a young female teenager (not a child but a teenager)