The pop star - who is engaged to DJ Tom Crane - wants to kiss goodbye to her single life with a Celebration in the gambling capital of America.
A source told the Daily Star newspaper: "Sarah wants a raucous hen weekend in Las Vegas with a selection of her most loyal girlfriends. A full on girlie blow-out is the perfect way for Sarah to bow out of her partying days."
While Sarah is planning to hit the clubs and casinos of 'Sin City', Tom is organising a quieter affair in the English countryside for his stag party.
The source added: "Tom's inner circle is planning a traditional country retreat for his friends and brother.
"The weekend will involve them getting dressed up in proper attire before spending time fishing, shooting and hunting. But there will still be plenty of boozing in the evenings."
Although they know what they are doing for their respective parties, the couple are said to be in disagreement over the type of nuptials they want.
Tom reportedly favours a "subtle English wedding", while Sarah is keen on having the ceremony "in a gothic castle".