Femininity and ‘‘Frivolous’’ Spending

The Girl Maths trend has maintained it's relevance on the internet for over a year now, being used as a tongue in cheek way for women to justify ‘’frivolous’’ purchases from iced lattes to designer handbags to Taylor Swift concert tickets. But why is it that women feel the need to justify their spending in this way? And why is it only costs associated with femininity that are deemed as ‘’frivolous’’?