Frida Kahlo's 1940 surrealist self-portrait "El sueño (La cama)" sold for a record $55 million at Sotheby's auction, setting the highest price ever paid for a work by a female artist.This price surpassed Georgia O'Keeffe's previous record of $44.4 million and was reached after a five-minute bidding war between two unknown collectors.Kahlo's painting reflects her trauma and fear of death, and the sale highlights the growing recognition of female artists in the high-end art market.