Diamonds are a crappy investment for anyone who does not understand the diamond business. If a woman were to invest in diamonds it would be crappy as well, because the wholesale diamond business is a guy thing for specialists only. But of the diamonds are free, then it is not crappy at all. I know of no rich women who used diamonds to rise to the top of any business, although perhaps there have been some. Rich women, of course, and unlikely to reveal that they got rich by golddigging, especially if they did.
Cut and unset diamonds of 2 and more carats, grades A B and C are generally regarded as "investment grade", small enough to smuggle out of any country in one's butt. Of course, one would use a container of bamboo, gutta percha or something else organic, as metal would be embarrassingly detectable. The anal capsule, described in the novel Papillion, was called a "plan", and rolled up, large denomination paper money was generally used to smuggle money in to Devil's Island Penal Colony, or so he says.
Papillon and excellent film with Dustin Hoffman and Steve McQueen. But the novel is better still. More detail.
If this were easy to do, drug runners would do it all the time. Who knows? Perhaps some do. They only catch the ones that are easiest to catch.