cornflake girl
The term comes from a song written by tori amos about betrayall between women. In the song two factions of women are referred to; the "Raisin Girls" are "multicultural" and open-minded while the "Cornflake Girls" of the title are "narrowminded and full of prejudice". This aludes to their distribution on a cereal box, then "raisin girls" are harder to find.
She will never accept your idea, she's a total cornflake girl