She looks like Tina Majorino
I was just watching Youth in Revolt and decided to look her up. I see other posts of people thinking she looks like Melissa Joan Hart or Thora Birch. Other than being blonde I don't see how she resembles them at all.
She has very cute rounded features and a perfect face for big smiles and grinning. I think her perfectly shaped body and face are more in line with Tina Majorino. Look up Tina Majorino's IMDB photos, Portia's photos from Youth in Revolt, and tell me if you agree or disagree.