Ooo. She should have her hair it's natural color more often. It looks good on her.

Rare image of Laura with natural hair color.

I like both colors, the purple makes her look younger

Oh, it's easy to make her hair color changing make sense in the story. Since they're traveling and trying to avoid cities as much as possible, she doesn't have any hair dye and it slowly grows out as they travel. You could start with gray roots that become longer and longer in each successive page until her hair is finally completely gray. (TBH, I kind of like her hair being gray.)