big girl refers to age & maturity.
Big girls don't always cry. They have mastered the art of silence, accompanied by a glare - hence the phrase "if looks could kill".
Sadly, despite many attempts to study this phenomenon, scientifically, there is very little data. Mainly because not many men survive that stage. However, many a myth has a grain of truth. Medusa had a very bad hair day but you don't hear of men that survive telling her that.