As the parent mentioned, if you go to Japan, you'll see a thriving market for manga that appeals to girls of varying age groups. So, this would lead one to believe that the demand exists now, it's just completely untapped here. (Ignoring possible cultural differences.) Do you know how you create a large comic book market for older girls / women? Get them hooked when they're young on age-appropriate material, treat them well, and you'll create that market.
Consider 'normal' books. Kids (including girls) have a wide variety of age-appropriate books in a large amount of genres to choose from. I don't understand how there could be a demand for these books, and not those same books with added pictures in them.
Fair enough. I didn't want to get into it because I wanted to keep my point succinct but I believe the main point still applies. You want to change the fact that in the US, comics are only for kids/nerds? Get kids involved early, don't alienate them, and what was once only for geeks and nerds will be for everyone.
Consider 'normal' books. Kids (including girls) have a wide variety of age-appropriate books in a large amount of genres to choose from. I don't understand how there could be a demand for these books, and not those same books with added pictures in them.