Anybody else wondering THIS....
If they really are the only 3 people on Earth the only way to rebuild the human race would be for her to crank out as many babies as she can maybe a couple dozen over many years and BOTH men need to have sex with her to provide as much genetic diversity as possible.
AND they need to get their children (I know this sounds sick) to have incest with each other and a lot of it, even though it is not that great for the gene pool for a few hundred years at least incest will have to be legal and encouraged.