Insiders say Lisa - the late Elvis' only child is desperate to protect her fortune after previous marriages failed.
The 38-year-old married musical director Michael Lockwood, 44, in a lavish $340,000 Japanese ceremony last month.
And sources say the mum-of-two is desperate to have more kids.
One pal said: "She swore the only reason she would get married again would be to have more children.
"She was hoping to be pregnant by the time they announced the wedding. "Only time will tell."
Lisa, worth a reported $952m, earns an estimated $8.2m a year from the tourism business surrounding Elvis' former home, Graceland.
She sold part of the lavish Memphis estate last year for $136m.
She met guitarist Lockwood two years ago but she insisted on the pre-nuptial agreement in case the union fails.
A source said: "However much she loves him, she has to protect her fortune."
American celebrity divorce lawyer Raoul Felder told the National Enquirer: "Because of her tremendous wealth, this would be the mother of all pre-nups."
Lisa Marie's new father-in-law told the magazine: "We're really happy.
"Lisa Marie is lovely."
She was previously married to Nicolas Cage and Michael Jackson. Her first husband and the father of her two children, Danny Keough, was best man at the ceremony in Kyoto on January 22.
One witness said: "You could feel the love.
"They were gazing into each other's eyes and stealing little kisses through the service."