My Daughter Has A Raised White Colored Spot On Her

My daughter has a raised white colored spot on her knee. I thought it was initially an infected poor, like a pimple, but it has raised more and never obtained a head. It has a solid feel to it and is round and raised. I'm thinking a wart but am not positive. She says it hurts when you push hard on it or if you squeeze from the sides, like trying to make a pimple pop. Any suggestions on what this is or how I should treat it?