When Daisy states this comment, she is indirectly criticizing the values of her time period. What she means is that intelligence is not a quality that is valued in women, and therefore, intelligent women are more likely to struggle in this world and to be unhappy. Daisy is aware of this, because she is playing the role of a hedonistic, silly, shallow woman in order to fit in society, but this is not her real persona. She believes that if her daughter is actually this way naturally, she might be able to find more happiness and acceptance than Daisy has been able to find in her life.
